David Cameron on Sunday ratcheted up the pressure on Gordon Brown over e-mails sent by a Downing Street aide, calling on the prime minister to apologise and guarantee the putative smear campaign against senior Tories would not be repeated.

Government insiders attempted to limit the political fallout, saying Mr Brown had already made clear he had no prior knowledge of the e-mails and condemned their content. “It’s damaging but it’s containable – we’ve done the right thing,” one aide said.