Warhol is turning in his grave.

The Pop Art Portraits exhibition on at London’s National Portrait Gallery, which features the work of influential Pop artists such as Larry Poons, Robert Rauschenberg and Andy Warhol, says a lot about the contemporary fixation with copyright.

Apparently they cut up magazines, copied comic books, drew trademarked cartoon characters like Minnie Mouse, reproduced covers from Time magazine, made ironic use of a cartoon Charles Atlas, painted over iconic photos of James Dean and Elvis Presley - and that’s just in the first of seven rooms.

We’ve all heard the Campbell’s Soup story haven’t we. Andy Warhol said anyone could make use of, or reproduce, his painting of the Campbell’s Soup can, without cost or royalty, so long as they gave him credit for the “work”.

But what did Campbell’s get from the deal?

Certainly no money changed hands (though I wonder what the value of the publicity created by Warhol would be worth?), and I’m not even sure Warhol asked to use the now iconic soup can image.

[They] created these images by nicking the work of others, without permission, and transforming it to make statements and evoke emotions never countenanced by the original creators.

Despite the flagrant disregard for copyright the works on display represent, exhibition organisers, ironically, are not allowing any photos to be taken.

The ban on pictures is meant to safeguard the copyright of the works hung on the walls - a fact that every member of staff I asked instantly confirmed.

One wonders what Warhol would make of such an imposition?