Gordon Brown has written personal letters to the senior Tories mentioned in controversial emails sent by his former aide Damian McBride.
Mr McBride was forced to resign yesterday after emails he wrote to former spin doctor Derek Draper about smearing senior members of the Conservative party became public.
Reports this afternoon suggest the prime minister has written to those mentioned in the emails, but is unclear whether they will include a formal apology.
Earlier, health secretary Alan Johnson and a spokesman for Downing Street had said there was no need for the prime minister to apologise over the emails.
A Downing Street spokesman said: "Neither the prime minister, nor anybody else in Downing Street, had knowledge of these emails.
"It is the prime minister's view that there is no place in politics for the dissemination or publication of material of this kind, which is why it is right that Mr McBride and Mr Draper took the decision not to publish this material and regrettable that others are choosing to do so."
Speaking to Sky News, Mr Johnson said no one in the cabinet knew about Mr McBride's tactics nor the exchange of emails and thus there was no need for a personal apology.
The health secretary said: "You will diminish the value of a public apology if on every single issue there has to be an apology from people who had nothing to do with the initiative in the first place.
"What the prime minister has made absolutely clear is that this is wrong. He has put out a statement."
A group of Labour MPs and cabinet aides also criticised the actions of Mr McBride, adding that it was causing serious damage to the party.
MP Tom Harris said the scandal was "sordid", adding that the party had no one to blame but itself.
He said: "We screwed up, big time. We have no one, absolutely no one at all, to blame for this but ourselves. The damage the Labour party and the government have sustained has been entirely self-inflicted
"The people behind this sordid little mess owe everyone named in these emails a very public apology," he said.
Tony Blair's former communications chief Alistair Campbell also criticised the emails as being in poor taste.
"On reading the emails [Mr McBride] sent, I was struck not just by their unpleasantness, but also by their incompetence," Mr Campbell said.
Hayes and Harlington MP John McDonnell said the row had dragged the party into the "gutter" and that such tactics were not the "Labour way".