By Emma Griffiths BBC News Online, London

More pictures from the wall

Hoardings hiding workmen digging up paving in front of the National Gallery are not usually one of Trafalgar Square's more popular attractions.

But visitors have been fascinated by the work in progress there this week.

Fifteen of the country's top cartoonists are attempting to create the world's longest cartoon strip over 90m of white hoarding.

From Boadicea getting clamped to aliens pondering the function of a crumpled Millennium Dome, the "history" of London is portrayed in waterproof black marker pen.

The cartoons have to tell a consecutive story if they are to meet the Guinness Book of Records' requirements.

They were certainly drawing a crowd of people to see a different view of London's history.

Comic timing - you can't beat the weather for it Cartoonist Hack

Marcel Jansma was escorting a group of Dutch students who had just asked whether that was Napoleon on Nelson's Column.

"It's too bad it's not finished because we could take our students past it and do a history lesson in one walk," he said.

Others were less certain about its historical accuracy.

Festival manager Mick Bateman who brought the plan to life with the help of London's poet laureate Martin Rowson, said: "It can be very confusing for tourists, who will be going home with a completely different idea of British history."

The cartoonists are racing against the clock and the weather to complete the strip by 1830 BST on Wednesday.

Tea towels are on standby to dry off the boards, although the pens are waterproof, they will not make a mark if the "canvas" is wet.

Pupils on school trips watched the artists at work

But the artists themselves did not seem to be put off by the showers.

"Comic timing - you can't beat the weather for it," said cartoonist Matt Buck, professionally known as Hack.

"Cartooning can be quite lonely - you tend to be locked in your office trying to be funny and you can go a little mad so it's quite nice to see people laugh at your cartoons."

Guardian cartoonist Nicola Jennings found the glare from the boards so bright she had to wear sun glasses while drawing the Great Fire of London.

"I thought I'd stay away from Livingstone and the congestion charge," she said.

Some tourist confusion

"A friend's coming down with a brolly to stand over me."

Those artists who could not make it in person have faxed through designs to be recreated by John Byrne and his team.

"It is the closest we will get to the National Gallery," he joked.

Much of London's history had a contemporary feel

Some tourists had difficulty understanding the satire, or the more contemporary references.

French teacher Peroud Jacques was admiring the Millennium Dome piece by Hellman, but was confused by the sponsorship banner for HM Prison Service above it.

"As a Frenchman I have got to think about it for a second time before I get it," he said.

He added: "I like this sort of English humour, it is a bit lighter - not aggressive."

The boards will eventually be auctioned off for Great Ormond Street Children's Hospital on the London Comedy Festival's website.