David Cameron has severed the Conservative party's ties to the Saatchi brothers' advertising agency, nearly 30 years after their "Labour Isn't Working" posters helped get Margaret Th-atcher elected.

David Kershaw, chief executive of M&C Saatchi, said yesterday that the agency had not worked for the Conservative party since last year. "Our subsidiary, the Immediate Sales Company, worked for the Tory party during the last election and were paid through the last election, and that's it," he said.