David Cameron sponsored a House of Commons pass for his communications chief Andy Coulson - which the former News of the World editor obtained without disclosing ongoing payments and benefits worth hundreds of thousands of pounds from the paper's owner News International.
Mr Coulson, who, it was claimed yesterday, is still having his legal fees paid by Rupert Murdoch's media empire, may have broken Parliamentary rules when he failed to declare his severance package on an official register at the time he obtained his first pass as a Tory Party employee in September 2007.
Under Commons' procedures, pass-holders must disclose details of paid employment, gifts or benefits worth more than £329 which could "in any way" relate to their work in Parliament.
At the time, Mr Coulson was receiving, from NI, health insurance, the use of a company car and the payment in instalments of two years' salary remaining on his contract following his resignation as NOTW editor in January 2007.
The revelation, reported by The Guardian, that Mr Cameron, then Leader of the Opposition, backed Mr Coulson's application for a pass, increases pressure on the Prime Minister over his decision to employ the former tabloid editor.
Tom Watson, the Labour MP, who has campaigned on phone hacking, last night wrote to the parliamentary standards commissioner making a formal complaint against Mr Coulson and calling for an investigation.
Mr Watson said: "When he applied for his pass, Mr Coulson was obliged to declare any payments or benefits he was receiving."