Andy Coulson appears to have broken House of Commons rules by failing to declare payments and benefits he received from News International while holding a parliamentary pass sponsored by David Cameron.
Registers held in the Commons archive, seen by the Guardian, reveal that in September 2007 – three months after Coulson was employed by Cameron's office – the former News of the World editor failed to declare the health insurance, company car and severance payments he was receiving from his old employers.
The records also show that for at least two months after he resigned from his position as No 10's head of communications in January this year, Coulson continued to hold a parliamentary pass, sponsored by Downing Street, which allowed him access to parliament as a No 10 employee.
That will raise new questions about whether Coulson – who Cameron has admitted seeing on a social basis since his resignation – continued to perform an unofficial role for the Tories after he had left.
Commons rules say all holders of parliamentary passes sponsored by MPs, which allow unfettered access to most of the parliamentary estate, must register any paid employment, gifts or benefits worth more than £329 they receive within that calender year from sources that could "in any way" relate to their work in parliament.
The Guardian also understands that News International continued to pay Coulson's legal bills after he stepped down as the editor of the News of the World in January 2007.
The company is considering ending the arrangement after this week's revelations that Coulson had continued to receive payments after becoming Cameron's director of communications.
Coulson is understood to have consulted lawyers frequently since leaving News International after several public figures brought civil cases against the News of the World, alleging that their voicemail messages had been hacked.
News International paid his legal bills last December when he was a witness in the perjury trial of the former Scottish MP Tommy Sheridan. The company declined to comment.
Cameron and George Osborne first employed Coulson when the Conservatives were in opposition in July 2007.
He appeared on the next register for MP-sponsored passes, published in September, declaring no other employment, gifts or benefits in that calendar year. It is now known that he received hundreds of thousands of pounds in "several" instalments from News International after leaving the company.
He also failed to register the health insurance and company car he received from the company under gifts or benefits.
Coulson's pass was personally sponsored by Cameron, not the Conservative party. His register entry noted only that he was director of communications and planning for the Conservative party, making no mention of any other income.
From October, his pass switched to a journalist's pass, sponsored by the Conservatives, which operated with a separate declaration register.
Declarations are only required of an "occupation or employment", earning more than £657 in that calendar year, that could be benefited from access to parliament.
For his entire period working for Cameron at Conservative campaign headquarters, and subsequently in Downing Street, Coulson declared nothing on the registers.
A Conservative spokesman said: "It is the individual's responsibility to declare relevant financial interests to the parliamentary pass office.
"We were not aware until Monday night of allegations that Andy Coulson's severance package, agreed with News International before he was employed by the Conservative party, was paid in instalments that continued into the time he was employed by the Conservative party."
Watson, a member of the culture select committee who has campaigned on the phone hacking debate, is writing to the parliamentary commission for standards to complain about the apparent breach.
"We now know that, in September 2007, Andy Coulson was receiving staggered payments, free private healthcare and apparently a motor car from News International," Watson said.
"When he applied for his House of Commons pass, Mr Coulson was expected to declare these hidden payments under parliament's transparency rules. He failed to do so.
"Moreover, instead of being allocated a political party press pass, he was placed on David Cameron's personal allocation of passes. This meant David Cameron had to personally vouch for his application, so presumably they had a discussion about it. I'm writing to the standards commissioner to request he investigates the matter."
Commons officials confirmed that it could take up to a month for people who hand their passes in to be removed from the register of journalists' interests.
Coulson resigned on 21 January and appears on the next two registers, published in March and April, but not from June. That suggests he could have continued to hold his Downing Street-sponsored pass up until May, four months after his resignation.
He resigned from News International after the jailing of two private investigators who worked for the News of the World, during his time as the paper's editor, for phone hacking.