After his triumphant Tate installation, The Procession, the artist is preparing a radical exhibition tackling Britain’s imperial past.He talks about why we must return plundered artefacts and rethink attitudes to heritageWithin the oak-panelled walls and glass display cases of the Enlightenment Gallery of the British Museum – a long, impossibly high-ceilinged room that is a temple to the gods of reason and imperialism – there is a little unmarked secret door, leading backstage or who knows where.You would never spot it unless you were looking.But for the rest of the autumn – for the first time in its 200-year history – that door will be symbolically flung open and three raucous figures will be emerging from it, invading the hushed space of marble busts and dinosaur fossils and leather-bound books.Leading the charge will be a young child of indeterminate heritage, in rags and patches, calling the others on.

The figures emerge not only from the secret door but from the imagination of the artist Hew Locke, who was recently sitting with me on a low leather seat nearby, one quiet early morning before the museum opened, explaining, with half a smile, how it will look.“There are three figures but the sense is that this is just the advance guard, there are hundreds more behind, you know, like a horde,” he says.“The child is holding a medal, an enlargement of a medal that was given to soldiers in east and west Africa, to the Benin expedition guys [who plundered that country’s riches].And he has a little armband with a very crude plastic replica of the Koh-i-noor diamond.It’s a mix-up, a messing around with colonial history, a messing around with ideas of the collection here.

”Locke turns 65 today, 13 October.A tall man, with a straggly mutton-chop beard and wise eyes, he has waited a working lifetime to do a bit of that mixing up.Born in Edinburgh to a black Guyanese father – the sculptor Donald Locke – and the white British painter Leila Locke, he spent his formative years in his father’s newly independent homeland before returning to the UK to study.When he arrived back here in the early 1980s he would, he says, often wander the rooms of the British Museum, “doing my thinking” – a habit that is nicely summed up in the title of his forthcoming revolutionary exhibition at the mother of all museums: what have we here?“I have been coming here for decades and decades,” he says, in a voice that still carries the leisurely cadences of Georgetown, Guyana.“I would find a place that was less crowded and just walk around and make up stories for my work, have ideas, forget ideas, imagine stuff, destroy plans, and somehow – through that process – something would stick.

”What sort of thing was he thinking back then?“I hadn’t really evolved my ideas,” he says.“But I grew up in a post-colonial society.I saw Guyana being created.I saw banknotes being created.I arrived just in time for independence, and knew what had been there before.

But then coming to London, I realised that although we [Guyanese] knew all about this place, this place didn’t know anything about us,And that was quite a shock, the lack of a two-way thing,”The stately marble halls of the British Museum, engine room of modern western civilisation, crystallised that thinking,Locke remembers a few formative realisations,Here’s one: why is Egypt never described as being in Africa? “A simple thing like that.

The answer, I guess, is because they wanted Africa to mean something different.And then you realise the fact that some of the Egyptian Pharaohs were Nubian, they were black men.And then after that, well, everything is up for questioning.”The Enlightenment Gallery, designed by Sir Robert Smirke in the 1820s, originally housed the library of the recently deceased King George III.It was conceived as the physical embodiment of the age of reason, the place where aristocratic British collectors dramatised their hierarchical view of the world and of human history, with themselves – natch – at the apex, in marble, on plinths.

The museum’s collection of objects began with the bequest of Sir Hans Sloane.His interest in bringing home treasures and curiosities from Indigenous communities and the classical world began when he worked as a physician on Jamaican slave plantations, the riches from which fuelled his compulsive collecting.A marble bust of Sloane – lately removed from its pedestal and housed in a cabinet – looks down on me and Locke as we are talking.“The Enlightenment room is acting as a bit of a trailer for the rest of my show,” says Locke.“It is a very important place – obviously – but seriously lacking in colour.

And I’ve always found that whole concept of enlightenment,” he stretches the word out, sceptically, “shall we say, interesting.Because these people weren’t very enlightened, or only narrowly enlightened.”It goes without saying, I suggest, that in every sense they saw the world in terms of black and (unblemished) white?“They did.I wrote a thesis back in the 1990s about how different the world we live in might be if all the original colourful paint had remained on Greek and Roman statues.” It’s funny, he suggests, that people are still so shocked by the idea that those white marble busts and figures of the Parthenon marbles (otherwise known as the Elgin marbles), for example – were coloured in.

“They just won’t accept it no matter how you try to sell it.”One ambition of Locke’s is to bring some of that colour back into the museum – not least the range of skin tones that classical statuary once embodied.His exhibition will be, you might say, something of a sequel, or endpoint, to the triumphant and carnivalesque figures in The Procession, which memorably weaved their way through Tate Britain two years ago (described in a five-star review by Laura Cumming as “a tremendous spectacle … and most profound endeavour”).In the process by which galleries and museums re-evaluate the colonial roots of their collections and thinking, Locke has become something of a Prospero figure, magicking up the stuff that dreams – and nightmares – of empire were made of.Key to the new show will be a series of 11 oversized sculptural figures called The Watchers, who will perch in the fabric of the museum, observing visitors as they wander.

“You’ll see them on top of the shelves and so on,” says Locke.“They’re watching your reaction, sometimes pointing at you, maybe judging you – or are they judging you? How complicit is the viewer in this place? Who is looking at who?”To create the exhibition, Locke and his partner, studio curator Indra Khanna, have been visiting the British Museum for more than two years, examining objects in the stores, working closely with more than 20 specialist curators.When I ask him if he had full access to the museum’s vast underground vaults, he laughs.“There’s a story,” he says.Three months after he began, headlines about the museum’s Greek and Roman antiquities curator Peter Higgs emerged, reporting his arrest for allegedly stealing more than 1,000 precious objects from those stores over a 30-year period, and putting some for sale on eBay.

(Higgs, who maintains his innocence, is being sued by the museum over the loss of the objects.) “Conversations about the collection kicked into a pretty high gear then,” recalls Locke.“And security too.I was like: OK, what did I agree to here?”That change of context didn’t stop him fossicking.“Sometimes I’d think, bloody hell, we’ve got to have that,” he says.

“For example, this Portuguese cannon, seized in Benin.A strangely beautiful thing … ” Locke has created evocative clusters of objects, inviting connections about empire and power.Many of the 100 or more items he has brought out from the back rooms were suggestions from curators, he says, who knew how their stories or provenance chimed with his desire to “pick at the scab” of where things came from, and how, and why.“They were all: ‘Have you seen this?’ – and there were some difficult stories, not all happy, joy, joy.Not at all.

”One good example of the complicated history of some objects is the Asante Ewer, a bronze jug made for Richard II in the 1390s, which at some unknown point in the subsequent years of Gold Coast trade and slavery ended up as a sacred object in the royal palace in Kumasi (in present-day Ghana) before being looted and brought home by imperial British troops in 1896.“It’s quite a thing,” says Locke, in passing, “to be doing a show in this place, where you openly use the words loot and looting in the description of certain objects.Because you can’t hide it any more.”Featuring four overlapping themes – sovereigns and icons of nationhood, trade, conflict and treasure – the exhibition offers visitors their own choice of route through it.His intention is to make what once seemed set in stone feel more provisional.

“The whole exhibition,” he says, “is designed to look in part like it’s a series of packing crates, alluding to storage, to transport.”I’m reminded of the last time I met Locke, back in 2015 in his south London studio, when he was preparing for a New York show loosely themed around migration, and was surrounded by a homemade flotilla of large improvised wooden boats, which were a kind of emotional imperative: the first, a replica of the imperial barge of the maharajah of Jaipur, he had made for his degree show at the Royal College of Art.“Here’s the thing,” he said then, “Guyana means ‘land of many waters’ – you are constantly aware of boats.I went to Guyana as a five-year-old kid on a boat.I came back here on a boat.

I went to Falmouth to study art based on the fact that it looked like something I knew.Every three years I would need, psychologically, to make a boat.You can’t say why one thing means something to you.It’s that mix of politics and the personal that you are looking for, so that it flows in and out.”He has subsequently channelled that internalised ebb and flow – the trade routes by which objects and people have travelled – in resonant ways.

The current show will feature, for example, Locke’s Souvenir series: reworked 19th-century mass-produced busts of figures from the British royal family, decorated by him with the paraphernalia of imperial rule, embroidery and jewels but also replicas of medals, coins and other souvenirs of overseas conflict,Did he, I wonder, start with a kind of disruptive wishlist at the museum?“There’s a limit to what you can do,” he says,“You know I can’t gut the Duveen Gallery and take out all the Elgin marbles and show it as it could be if – and when – they go back to Greece,”Were there frustrations?“You start with, like, how far can I push these guys?” he says,“From the institution’s point of view, their reputation is on the line; and from my point of view, my reputation is on the line.

”Locke’s intervention at the museum comes at a critical time in these debates over provenance and ethics and ownership.“We live in a different world to the pre-pandemic world,” he suggests.“Pre-pandemic, everybody tried to talk a good game about decolonising the museum and stuff like that.Since the pandemic and Black Lives Matter, people think: ‘Well, hang on, we have to put our money where our mouth is.’”Sign up to ObservedAnalysis and opinion on the week's news and culture brought to you by the best Observer writers after newsletter promotionLocke’s exhibition is the first under the stewardship of the museum’s new director Nicholas Cullinan – who recently oversaw the inspired revamp of the National Portrait Gallery – and who has spoken of how “this universal museum is not [yet] universal enough”.

Cullinan has inherited the show, so is he fully on board with all its themes?“We haven’t completely had that type of conversation,” says Locke.“But we have bonded on certain things, for sure.” He agrees that it marks more than a moment; it is the beginning of irreversible re-evaluation.“And to be fair, despite my critiques of institutions like this over the years, it’s a brave thing to do, because you are not quite sure where it’s going to end up.”By way of example, he points to the Taíno carvings – 15th-century wooden sculptures from Jamaica of which the British Museum holds nine examples.

“For Jamaica this is the Elgin marbles, you know, they want them back.There are lots of debates that will be had in the future.”One of his aims is to give a sense of the sheer volume of such treasure that the museum holds from the former pink parts of the globe, much of it never on display.“I wanted the show to feel full of stuff,” he says.“So it doesn’t become an academic exercise aesthetically.

” Locke deconstructs the idea that the museum is orderly and academic as a post-rationalisation of the looting it partly represents.“If you work here, you obviously love the objects – but the way you display certain things, like a display of gold coins or something like that, is restrained.It wouldn’t be, let’s have 500 of them – that’s more an artistic approach.But when you’re invading a country or taking over a civilisation, shall we say, you definitely want plenty.You want all the gold you can grab.

You’re not really concerned about what this means, culturally or whatever – bollocks to that.”He recalls his partner, Khanna, talking about watching Antiques Roadshow.“People would always be saying, oh, I went up into the attic and I found this thing that great-uncle so-and-so picked up in this colony.And the antiques expert would say this is a wonderful example of this or that.And then it goes into auction, bish, bosh, done.

I don’t think you can do that any more.These days, the first thing people might think is, where did it come from? That question is going to be asked more and more.”I remember talking to former British Museum director Neil MacGregor about these issues ages ago, I say, and his argument, broadly, was that the museum was the world’s memory bank, the place where people from the world’s four corners make connections about shared history.Is what he is doing another expression of that idea?“Yes,” he says.“From a museological point of view, this could be seen as the world’s problem.

You can ignore it.You can bury your head in the sand.But as soon as you start looking and thinking, the whole thing becomes highly political.I was on holiday last year in Athens and went to visit the Parthenon Gallery.I was walking around thinking: ‘Shit, this is the most political museum I’ve ever been in.

’”In what sense?“There were all these casts of the Elgin marbles interspersed with the odd few they managed to hang on to.My wife was walking behind this American tour group and she heard someone say, ‘God, what must it be like to be British walking around here? Imagine the guilt.’ But that’s the same for any encyclopedic museum in Europe or America.There are certain things you expect to see, and now all those things are problematic.What do you do? If I was a young lawyer, I’d be thinking, ‘Boy, let me go into property law of this nature, there is going to be work for me for a long time