Tate Britain is home to the national collection of British art. It draws an average of 4,600 people a day to wander the pristine Duveen Galleries and contemplate masterpieces by Turner, Francis Bacon and Sir Joshua Reynolds.

Over in Trafalgar Square, some 4,400 a day stream into the National Portrait Gallery to rub shoulders with its roster of starry subjects.

For a few days this month, both these blue-chip cultural attractions were outperformed by a distinctly down-at-heel venue. Their rival? A temporary exhibition in an unlovely London tunnel described by one art critic, Shirley Dent, as “Piss Alley”.

During the Bank Holiday weekend, 9,500 people a day descended on Leake Street, near Waterloo Station, to see the Cans Festival, the subculture blockbuster of graffiti art organised by Banksy. Nearly 500 of them added their own stencils to the pieces by Banksy and the 38 other artists from around the world he invited to take part.

And although the exhibition officially closed at the end of the Bank Holiday, the paintings are all still up there on the walls - and a steady stream of people has been turning up to see them. Some of the works have been stolen, too: a couple of grafitti pieces - neither of them by Banksy - were painted on to metal doors that enterprising street art collectors quickly nabbed.

What remains of the exhibition should stay open to the public for a little while yet. The Department for Transport has taken over responsibility for the tunnel from Eurostar. A spokesman said: “We agreed a six-month period so that more people can see the work first hand. After this time, we will look at the best use of the tunnel.”