The gallery also announced that it is expanding its building and artistic collection to include works from the 20th century and beyond, following two donations of £150 million.

Entitled Project Domani (‘tomorrow’ in Italian), the new wing will be designed by the winner of an international architectural competition run by Colander Associates. The deadline is 17 October, and a shortlist will be announced on 28 November.

The winner is hoped to be announced next April, with a target opening for the building in the early 2030s, according to The Times.

Billed as the gallery’s largest transformation since its formation 200 years ago, its launch comes after the gallery’s controversial Sainsbury Wing was reconfigured and reopened in May, designed by Selldorf Architects.

National Gallery Sainsbury Wing

The funding for the latest project has been largely secured by two £150 million donations from Crankstart, the charitable foundation of billionaire Michael Moritz, and from the Julia Rausing Trust.

A further £75 million has been pledged from the National Gallery Trust, National Gallery chairman of trustees John Booth, and various anonymous donors, bringing the current total to £375 million.

Gallery director Gabriele Finaldi said: ‘With the bicentenary celebrations now completed, the National Gallery looks to the future.

‘We want to be the place where the UK public and visitors from across the globe can enjoy the finest painting collection in the world, from medieval times to our own, in a superb architectural setting.’

The extension will be built on the site of St Vincent House, a late-1960s concrete office block by Charles Pike & Partners, which sits to the north of the main building. It will be the third and final stage of a redevelopment masterplan launched by the gallery in 2018.

The scheme is also set to ‘revitalise’ the area between Leicester Square and Trafalgar Square, intending to deliver a ‘vibrant, fresh experience for visitors’.

In broadening the range of the gallery’s collection beyond the current cut-off date of 1900, the museum will work with the Tate as ‘joint custodians of the National Collection’, with a meeting to ‘establish a working group’ already being held.

Culture secretary Lisa Nandy said: ‘I’ve been clear that we want the arts to be accessible for everyone and that philanthropy is crucial to that mission.

‘The new wing at the National Gallery will open up world-class art for millions of people from home and abroad.  I want to thank the generous donors who will help to transform the National Gallery, cementing its position as one of the most loved and visited institutions that will inspire people for generations.’

Gabriele Finaldi told The Times that should the project require more funding, there were ‘no red lines’ in terms of who the gallery would accept money from – except, he said in an interview in July, the porn industry – and that donations were decided on a ‘case-by-case’ basis.