David Cameron will today be forced to explain damaging new revelations that have dragged him deeper into the phone-hacking scandal.
It emerged last night that Neil Wallis, the former News of the World deputy editor who was arrested last week, worked for the Conservative Party before last year's election.
He gave "informal" advice to Andy Coulson, his former boss at the NoW, who resigned from the paper over the hacking affair but was later appointed Mr Cameron's director of communications.
In a second blow to the Prime Minister it was revealed that his chief of staff, Ed Llewellyn, had appealed to Scotland Yard not to mention hacking during a Downing Street briefing last September, four months before Mr Coulson quit his No 10 post.
Labour said the disclosure showed Mr Cameron could not do his job properly because of the cloud cast by the controversy.
Mr Cameron returned last night from a trip to Africa he was forced to cut short by the crisis which some Tory MPs fear is in danger of destabilising his premiership.
Loyalists within his party believe the Prime Minister looks increasingly isolated and are concerned that Cabinet members, including the Chancellor George Osborne and the Tory chairman Baroness Warsi, have failed to rally behind him while he has been away.
But one backbench leader said: "The feeling is that this is a crisis of his own making - he employed Andy Coulson."
The Prime Minister's plan to go on the offensive today during a Commons statement on the affair suffered a setback with the disclosure that his party had links to two people arrested during the current police investigation - Mr Coulson and Mr Wallis.
A Tory spokesman said: "We have double-checked our records and are able to confirm that neither Neil Wallis nor his company has ever been contracted by the Conservative Party, nor has the Conservative Party made payments to either of them.
"It has been drawn to our attention that he may have provided Andy Coulson with some informal advice on a voluntary basis before the election. We are currently finding out the exact nature of any advice."
The Tories insisted that neither Mr Cameron nor any senior member of the party's campaign team were aware of Mr Wallis' involvement until this week. It is believed the advice was given on a one-off project during 2009.
Mr Llewellyn has already been accused of not passing on to Mr Cameron warnings from senior Lib Dems and newspaper executives not to appoint Mr Coulson to No 10 after last year's election.
Yesterday it emerged that Mr Llewellyn sent an email to John Yates, the former Metropolitan Police assistant commissioner, last September, saying he "would be grateful" if hacking were not raised by him during an imminent briefing on national security.
"I am sure you will understand that we will want to be able to be entirely clear... that we have not been in contact with you about this subject," Mr Llewellyn wrote.
The briefing was held shortly after allegations in the New York Times that Mr Coulson knew about hacking while he was NoTW editor and "actively encouraged" it, claims he denies.
Cameron aides said the plea was nothing to do with Mr Coulson but reflected a desire that politicians should be involved in operational police matters.
However, Mr Llewellyn's request appears to have been in the mind of Sir Paul Stephenson, the Met Commissioner, when he decided last week not to tell Mr Cameron or the Home Secretary Theresa May that Mr Wallis had been employed as a PR adviser to Scotland Yard - a role which contributed to Sir Paul's decision to resign on Sunday.
Mr Cameron has expressed surprise he wasn't told about Mr Wallis' police link and Ms May said the Government was not told earlier.
Mr Yates confirmed to the Home Affairs Select Committee that Mr Llewellyn made the request.
"Ed for whatever reason - and I completely understand it - didn't think it was appropriate for him, the Prime Minister or anyone else in No 10 to discuss this issue ... and [said he] would be grateful if it wasn't raised."