Big Draw launches in London

Cartoonists (left to right) Posy Simmonds, Steve Bell, Peter Brookes and Michael Heath draw cartoons at the launch the Big Draw weekend at City Hall in London Photograph: Peter Macdiarmid/Getty Images

Tim Sanders (R) draws a cartoon watched by fellow cartoonist Michael Heath Photograph: Peter Macdiarmid/Getty Images

Michael Heath draws a cartoon at the launch of the Big Draw weekend Photograph: Peter Macdiarmid/Getty Images

London mayor Boris Johnson admires a sketch as he stands with cartoonist Posy Simmonds at the launch of the festival Photograph: Peter Macdiarmid/Getty Images

Boris Johnson shows off a drawing he made at City Hall after taking lessons from Britain's top cartoonists including (left to right) Steve Bell of the Guardian, Charles Peattie of the Daily Telegraph, Tim Sanders of the Independent and Michael Heath of the Spectator Photograph: Stefan Rousseau/PA

Steve Bell draws a cartoon inspired by the recent public sector cuts on the top floor of City Hall as part of the Big Draw Photograph: Sarah Lee for the Guardian

Posy Simmons draws a cartoon, while girls from Mulberry school in Whitechapel practise their draughtsmanship Photograph: Sarah Lee for the Guardian