It measures 6x3m and was printed by Nottingham-based The Art Department with pre-press work carried out by Sheffield firm Create 3D. Creative work was by the Conservative Party's agency Immediate Sales.

The poster is positioned on the A4 in West London, and depicts a smiling Tony Blair. As motorists pass it changes to show a serious Prime Minister alongside the tagline "Wipe the smile off his face on 5 May".

"This project took a lot of forethought and it was quite a pioneering job," said The Art Department director Bryan Ayres. "It was printed using a re-calibrated, ink-jet press."

"We felt that it very much fitted in with the campaign message," said Immediate Sales chief executive Michael Moszynski. "It works in terms of traffic flows and direction. We worked very closely with Creative 3D on this project."

Ayres added that there were other projects in the pipeline between The Art Department and Create 3D.

Story by Philip Chadwick