Gabriele Finaldi could be forgiven for nipping off for a two-month break to read about medieval English art, as he is about to do. After all, the director of the National Gallery has just hosted a year-long celebration of the museum’s bicentenary, an acclaimed revamp of its Sainsbury Wing and a comprehensive — and great — rehang of the entire collection.

But before he heads to Massachusetts, Finaldi has an important announcement to make. Today he is unveiling Project Domani (“tomorrow” in Italian, perhaps a nod to his heritage) — a new wing that will open up the gallery’s north-south axis, between Leicester Square and Trafalgar Square. An international architectural competition to design the most significant new museum building in central London since the Tate Modern extension, Switch House, launches this week.

But that’s not all. Today the National Gallery also announces a change to its collecting and display policy. No longer will the museum limit itself to works created before 1900, as was agreed (pretty informally, it turns out) at the turn of the millennium between Neil MacGregor, then director of the National Gallery, and Nick Serota, then director of Tate — two big beasts taking pains not to tread on each other’s toes.

“It’s very nice to be thinking about the future after the bicentenary,” Finaldi says as he leads me to a hidden bench on the bridge where the Sainsbury Wing meets William Wilkins’s original 1838 building. Our view is a jumble of the Sainsbury, the Wilkins and St Vincent House (known as SVH), a tired 1960s building behind the gallery that houses a hotel, rented office spaces and the gallery’s technology-in-exhibitions department.

SVH was acquired at the end of the Nineties “with a view to future development” but plans have crystallised as part of an ambitious masterplan commissioned in 2018. The architectural competition will run to October 17, with a shortlist announced on November 28. The gallery hopes to announce the winner in April next year and open the new building in the early 2030s.

Any fears that fundraising would be compromised by the refurbishment of the Sainsbury Wing have been comprehensively allayed by the astonishing sum already pledged, £375 million, which includes the two largest publicly reported single cash donations to a museum or gallery anywhere in the world: £150 million each from the Crankstart Foundation (the charitable foundation of Sir Michael Moritz KBE and his wife, Harriet Heyman, who have funded the Booker and International Booker prizes since 2019) and the Julia Rausing Trust.

“It turned out to be the other way around,” Finaldi says. “The confidence that you can have in an institution, I think, was only raised by the success of the bicentenary year. These are absolutely extraordinary gifts and they express a remarkable confidence in the National Gallery and our plans.

“These are huge, huge donations, of a different order to anything we’ve seen before. We’re still absorbing the significance of it and we’re very conscious of the responsibility that places on us to do something significant and, of course, very long term.”

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The other £75 million is coming from the National Gallery Trust, the gallery’s chairman of trustees John Booth, and other donors who wish to remain anonymous. Project Domani’s final cost will “depend on what kind of building emerges” but, for comparison, the V&A East Storehouse, London’s most recent museum development, was costed at about £63 million when it was announced (the final figure has yet to be confirmed).

The National Gallery’s NG200 refurbishment project cost £85 million. The Museum of Modern Art in Warsaw, an entirely new building also built in the centre of a historic city, cost about £100 million. If the National does need to raise more, Finaldi has said he doesn’t have red lines (the British Museum has been criticised for accepting £50 million from BP for the renovation of its Western Galleries). When I spoke to him in July he didn’t rule out taking money from any sector except “the porn industry”, adding, “We take it on a kind of case by case.”

Tate is on board with the shift to exhibiting post-1900 art, Finaldi says. A working group of trustee and curatorial representatives from both organisations has been set up, according to a statement from the Tate director, Maria Balshaw, “to determine the ways in which we can collaborate to further the national collection as a whole”.

Cubist painting of fruit, bottle, and violin.

Fruit Dish, Bottle and Violin by Picasso; the gallery will add significantly to its collection of post-1900 art

SUCCESSION OF PICASSO/DACS/THE NATIONAL GALLERY LONDON

In any case, it’s not as if the National hasn’t paddled in modern waters before, with commissions such as the magnificent Paula Rego that hangs in the Sainsbury Wing restaurant and exhibitions about the influence of Piero della Francesca on David Hockney. There are already 25 post-1900 works in the collection, including a couple by Picasso and four by Monet.

“We are a museum of painting, not a museum of art in general — it’s natural for us to want to continue telling the story of painting,” Finaldi says. “Ultimately it’s for the benefit of the national collection and for the UK public. We work very closely with sister institutions but there are opportunities for us to do more together.”

He says that “given the cost of the kinds of works that we’re talking about” — 20th-century masters are notoriously pricey — the increasingly popular wheeze of co-acquisitions, such as that of Joshua Reynolds’s Portrait of Mai by the National Portrait Gallery and the J Paul Getty Trust, will form part of their strategy. And if the collection is to grow, “what we’re very clear about is that we need space for pictures,” Finaldi adds.

It’s a tempting brief for any architect, a simple one that offers significant freedom. “It will develop as time goes on but it’s about creating display space, about making good use of daylight, about building something which is distinguished and beautiful,” Finaldi says. “It’s about something that recognises the importance of the setting and of the surrounding National Gallery buildings. That’s essentially it, at the moment.” It’s not quite it: Finaldi adds that he would like to “incorporate some kind of energy centre that could benefit the entire estate”.

There is also the impact of a site that spans 2,295 sq m — just a little less than the Sainsbury Wing — on the public space that surrounds it. “You can’t just think about the inside, you have to think about what a development of this kind can do for this bit of central London,” Finaldi says. The road behind the gallery “is essentially a rat run for taxis”.

There are plans, led by Westminster Council, to develop the area, which also includes the National Portrait Gallery and is fringed with theatres, as an arts quarter, he says (though it’s not as yet entirely clear what that means). “And we want to play a significant role in that. This is an important part of town — the opportunity to turn it into prime cultural urban space is very exciting.”]]

There is a hope, he says, that the new building might allow easier access to works that are at present in store. There was a minor furore recently when the art dealer Angus Neill complained that his donation, a Christ Carrying the Cross attributed to the workshop of the 15th-century Venetian painter Giovanni Bellini, was no longer on display following the recent rehang. Neill told The Times’s Richard Morrison that he had obtained assurances at the time of the donation that the picture would remain either “on permanent public display” or “readily accessible as part of its reserve collection”.

Painting of Christ carrying the cross.

Christ Carrying the Cross, attributed to the workshop of Giovanni Bellini, was recently removed from display

All the National Gallery’s holdings are stored on site, Finaldi assures me, and can be accessed by appointment by any member of the public if it is conservationally safe to do so. “Because these pictures belong to the UK public. They have a right to see them.”

Neill’s donation “is here”, he adds. “It’s being looked after and it will be on show at some point in the future. I can’t say when but pictures are not necessarily always on display on the main floor unless they’re great masterpieces.” Finaldi manages not to make this sound pointed.

For him, the thrill of the new announcements is tempered in the nicest possible way by his own plans: an unorthodox but well-earned study break at the Clark Art Institute in Massachusetts. After ten years in post, and a period of enormous change, he’s champing at the bit to spend a precious few weeks having a change of pace.

And he’s timed it well. There are now about 1,000 paintings on display at the National Gallery, up from about 600, while the redevelopment has precipitated a 60 per cent increase in visitors since May. Nobody wants another Louvre (too big, too many people), but this new development could supercharge visitor numbers and London’s economic and cultural heart. So Finaldi can trot off on his sabbatical with some satisfaction, and a lot of excitement for the future.