A sketch which ended up as this piece in north London was auctioned
Graffiti star Banksy's secret identity caused some problems for Labour's accountants, after he donated a piece of art to raise funds for the party.
The piece, Sketch for Essex Road, was the star lot at a private fundraising auction at a gallery, raising £195,000.
But the party could not accept the full sum as there was no way of checking Banksy was a "permissible lender".
The party gave £75,000, the original valuation of the piece, to the gallery and accepted the remaining £120,000.
There are various rules governing who can donate sums of more than £200 to UK political parties - for example individuals must be on a UK electoral register.
But Banksy, whose stencilled artwork appears in public places around the world, has never confirmed his identity - despite newspaper reports claiming to have unmasked him.
When the Aquarium Gallery, which held its own artbid4Ken fundraising auction for Ken Livingstone's unsuccessful London mayoral campaign, handed over the money raised, the Labour Party could not accept it in full.
After discussions with the Electoral Commission, the party decided to accept a cheque from Steve Lazarides, a gallery owner who deals in Banksy works, for £121,600 of the £195,000 he paid for the piece.
The reasoning was that by not accepting the £75,000 the piece had been valued at, they were effectively writing off the value of Banksy's donation, which they could not accept.
Sketch for Essex Road is a canvas depicting two children pledging allegiance to a Tesco carrier bag hoisted on a flagpole.
Another version of the image was eventually painted on the side of a pharmacy in Islington, north London.
A Labour spokesman said the party was satisfied all donations fully complied with the law.
He added: "We sought guidance from the Electoral Commission on this issue and we are fully satisfied that this donation complies with the rules.
"Obviously we carry out diligent checks on all donations and take care that we are fully compliant with the law. "
The Labour Party faced embarrassment last November, when it emerged one of its biggest donors, businessman David Abrahams, had given it more than £600,000 over four years - using other people's names.
According to Electoral Commission figures out this week, Labour's debt stands at £17.9m, the Conservatives' at £12.1m and the Lib Dems' at £1.1m. Steve Lazarides was listed among Labour's donors.