Scotland Yard has been asked to investigate new claims of phone hacking after it emerged Gordon Brown and Tony Blair could have been victims while they were in Downing Street.

A source close to Mr Brown confirmed he had written to the Metropolitan Police over concerns he was targeted when he was Chancellor of the Exchequer during the latter stages of Andy Coulson's reign as News of the World editor.

And although Mr Blair's lawyers denied he had contacted Scotland Yard, Labour sources say the former prime minister had concerns about the security of his phone and the phones of his inner circle.

Mr Brown's concerns centre on a period between 2005 and 2007 when he feared voicemail left for him and messages he left for other people were being hacked into.

They are the most high-profile public figures to be drawn into the controversy, and senior politicians from both Government and opposition combined to demand the allegations were fully investigated.

Labour deputy leader Harriet Harman said the law must be enforced while the LibDem Energy Secretary Chris Huhne said it was "implausible" to claim the practice was confined to "one rogue reporter" at the News of the World.

Ms Harman said: "Hacking into people's phones is illegal. Obviously the criminal law has got to be complied with and if it is broken then it should be investigated by the police and it should be enforced. Nobody is above the law: no newspaper editor, no journalist."

Mr Coulson resigned on Friday as David Cameron's director of communications amid continuing allegations of phone hacking among the paper's journalists while he was in charge, though he has always denied any knowlewdge of the practice while he was at the helm.

Mr Huhne said the phone hacking extended far beyond the News of the World's former royal correspondent Clive Goodman who was jailed in 2007 along with private investigator Glenn Mulcaire.

He said: "I have worked on a newspaper and I have been a journalist and it does seem to me totally implausible that this was a situation where it was limited to one journalist.

"I was rather surprised that the police seem to have accepted that story rather than investigating further."

Scotland Yard formally closed its investigations into the allegations against the News of the World last month and has declined to comment on the latest allegations.

However, senior officers are expected to come under fire when they are questioned about the hacking by the London police authority this week.

MPs are also taking evidence for a parliamentary inquiry into the scandal and the Department of Public Prosecutions is to meet senior officers to discuss the evidence.

Deputy First Minister Nick Clegg yesterday denied the Government had been damaged by the row over Mr Coulson. He said Mr Coulson had denied knowledge of any hacking when he was editor and Mr Clegg said he had "no reason to disbelieve him".

Mr Clegg defended the Prime Minister's handling of the issue and his decision to appoint Mr Coulson. He said: "If you listen to what David Cameron has said, he said very emphatically that he thought it was right to give Andy Coulson a second chance.

"Andy Coulson has been very clear that he was not in any way responsible for phone hacking and had no knowledge of it. I have no reason to disbelieve him."

Mr Clegg also said he would have some input into who would replace Mr Coulson. He said: "It is primarily a decision for the Prime Minister, [Coulson] is the Prime Minister's spokesman, but he is also responsible for communicating policy so of course I will have a role to play."

Tommy Sheridan, who will be sentenced on Wednesday after being found guilty of perjury in a case involving the News of the World, has already called for a re-examination of the evidence.

Sheridan is planning legal action against the paper after his personal details emerged in a phone-hacking investigation.

He has instructed his lawyers to pursue the paper and a private investigator for breach of privacy.

A string of other celebrities have also said they believe their phones were hacked into, including actress Sienna Miller, former Rangers footballer Paul Gascoigne, Sky Sports commentator Andy Gray and comedian Steve Coogan.