Mr Conway is to stand down at the next election
A standards watchdog has ordered MP Derek Conway to return £3,757 of taxpayers' money used to employ his elder son Henry as a researcher.
He was also told to make a written apology to the House of Commons by the Standards and Privileges Committee.
It said Mr Conway had made a "serious lapse" of judgement in overpaying his son while he was a student in London.
The MP said he would comply but added the committee had given a "subjective opinion, made with hindsight".
Mr Conway was suspended from Parliament last year for paying younger son Freddie to work as a researcher while he was a student in Newcastle.
He also had to repay £13,161 and make an apology on the floor of the House of Commons.
'No hard evidence'
The committee has released its latest report, on payments to Freddie's older brother, Henry, following a complaint from Labour MP John Mann.
It notes that Henry worked for his father from 1 July 2001 to 1 October 2004, during which time he was paid £35,744 before tax.
The committee says: "While we note that there is more circumstantial evidence of Henry Conway working for his father than there was in the case of Freddie Conway, it is unfortunate that there is no hard evidence."
The report also says: "However, Henry Conway was a student at the Courtauld Institute of Art near Westminster; he lived at his parents' flat in Westminster; and he was seen about the Palace of Westminster on several occasions."
The committee said it would be "unfair" to suggest Henry had not done any work, but it added that he had been paid £3,757.83 over the normal rate for someone with his level of experience.
He had started on the correct wage but had been overpaid for most of his time as his father's researcher.
The report said: "This case has demonstrated a serious lapse of judgement by an experienced Member of the House.
"Nevertheless, considering it on its own merits, we conclude that a further period of suspension from the House would be a disproportionate sanction to impose."
It also said: "As he himself recognises, Mr Conway's political career is over."
MPs will vote on whether to impose the punishments recommended by the committee.
In a statement, Mr Conway said: "Henry was employed on the lowest grade of researcher/parliamentary assistant and over the 39 months employed was, on average, at the mid-point pay-scale within that grade.
"However the committee considered that he should have been at the entry level with a 2% annual uplift for the duration of his employment.
"The committee has applied a judgement on the guidance to members which requires costs to have been 'necessarily incurred' and from the outset I have maintained that this is a subjective opinion, made with hindsight and that I had complied with the rules which existed at the time."
He said the committee was within its power to reach such an opinion and he had complied with its request to write to its chairman, Tory MP Sir George Young, apologising for the breach of the 'necessarily incurred' rule.
During House of Commons business questions, Labour MP Fiona McTaggart said Mr Conway had brought the House "into disrepute".
Commons leader Harriet Harman said the public would ask "quite rightly" just "how much money will MPs have to take out of the public purse" before being forced out.
David Heath, who shadows Ms Harman for the Liberal Democrats, said the committee had gone out of its way to be "fair and understanding to Mr Conway."
He added: "He should now accept these findings and immediately pay back the public money which he has been judged to have used improperly.
"This has clearly been a bad week for the reputation of Parliament. We need to completely reform the way politics is done in this country."
Mr Conway, MP for Old Bexley and Sidcup, has already lost the Conservative whip and has said he will stand down at the next general election.