There were tensions, however, between the pressures for a major residential development and the provision of commercial office buildings that would earn income. The battle was hard-fought in the 1950s until the government supported the City’s desire for an enlightened environment that would support residents, education and the arts.

These were heady days for urban planning and cultural development. The formation of the Arts Council in 1946, the creation of new festivals and the belief in “arts centres for all”, led to a utopian desire to provide the best facilities, accessible to everyone, and the architects Joe Chamberlin, Geoffry Powell and Christoph Bon proposed a scheme with a significant arts component.

This was enhanced still further following a report by the opera producer and director Anthony Besch, who argued strongly for world-class facilities of substantial size – from the proposed hall of 1,300 seats and theatre of 800, he argued for a hall of 2,000 and a theatre of 1,500, somewhat optimistically arguing that this might enable them to make a profit. (Hope, as in so many artistic budgeting matters, sprang eternal.)

One consequence of the inclusion of major arts venues in the evolving design of the Barbican, given the fact that the outline of the scheme was already designed and the massive residential towers were already being built, was that the expanded theatre and concert hall both had to be placed underground and were consequently invisible to approaching audiences.

A quirky 1969 film about the Barbican project made for the City features a dialogue between two unseen observers: “An arts centre in the City – it’s going a bit far, isn’t it?” To which the answer is: “The arts centre is simply one part of the whole concept which couldn’t really flourish without the others. Together they’ll make not just another place to live, but a fuller way of life.”

And so it has proved across the years. Even the venue’s brutalist architecture, which was all the rage when the Barbican was conceived, but out of fashion by the time it actually opened, is finally being taken seriously. Now Claire Spencer, from Melbourne, will take the centre to its next stage as chief executive officer, reflecting the full diversity of the capital as it has changed across 40 years – and the long-promised Elizabeth Line will finally open this year, providing new transport links and connecting London east to west, with stations on each side of the centre. The Barbican will never again be difficult to find.

Nicholas Kenyon was managing director of the Barbican Centre 2007-21. ‘Building Utopia: the Barbican Centre’ edited by Nicholas Kenyon (Batsford, £40) is out now