A senior Conservative MP paid £50,000 of public money to his “all-but-invisible” son in a use of parliamentary allowances that approached corruption, a Commons watchdog has found.

Derek Conway was accused by the Commons Standards and Privileges Committee of risking the reputation of all MPs, and it recommended that he be suspended for ten days and repay up to £13,000.

The MP for Old Bexley and Sidcup faces the threat of deselection as he heads for a showdown with his local association, where senior members have voiced dismay at his conduct.

Mr Conway was found guilty of a serious breach of the rules after the Parliamentary Commissioner for Standards concluded that Frederick (Freddie) Conway, a full-time university student, had not fully earned either his £11,773-a-year salary or a series of bonuses of slightly more than £10,000, paid to him out out of the MP’s parliamentary allowances.

That triggered yesterday’s devastating report from the Standards and Privileges Committee, the cross-party body of MPs that is the ultimate arbiter of Commons rules.

“This arrangement was, at the least, an improper use of parliamentary allowances: at worst, it was a serious diversion of public funds. Our view is that the reality may well be somewhere between the two,” it concluded.

Freddie Conway was 19 and about to start an undergraduate course at Newcastle University when he was appointed part-time research assistant to his father in September 2004. He was paid for the job from Mr Conway’s parliamentary allowance until August 2007. Previously his older brother, Henry, had been paid £10,000 a year under the same arrangement. Mr Conway’s wife, Colette, is also paid out of his parliamentary allowances.

The committee said it was “astonished” by the lack of evidence of any work that Mr Conway’s second son had done in return for the £45,000 in salary plus pension payments he had been paid. “We note that FC [Frederick Conway] seems to have been all but invisible during the period of his employment. For the majority of that time he was based at Newcastle where he was engaged in a full-time degree course at the university. He had little or no contact with his father’s office, either in the House or the constituency.

“No record exists of the work that he is supposed to have carried out, or the hours kept. The only evidence available to us of work carried out was that provided by FC and his family.”

In his apology at the Commons, Mr Conway said that “no judgment from any quarter could be more harsh than that which I apply to myself.

“In apologising to the House, I would also like to apologise to my constituents and to the Old Bexley and Sidcup Conservative Association, which has been so very supportive to me and my family throughout a very difficult period.”

Alf Catterall, a member of the executive committee of Mr Conway’s association, said that the fate of the MP would be discussed next month. “I think he’s been very foolish thinking that he was going to get away with it,” he said. “It’s one thing employing members of your family it’s quite another if you can’t show they’ve done any work.”

Times Recommends

• How I lost the gift of joy for a while
• Why Ann Widdecombe has got it wrong
• Alas, it’s the end of the road for petrolheads