The father of David Laws says the MP returned to government "too soon" after resigning over his expenses and that he was "lucky" not to have been sent to prison.
Tony Laws, estranged from his 46-year-old son, spoke weeks after the Lib Dem returned to government as Schools minister with a seat at the cabinet table.
Mr Laws resigned in May 2010, just 17 days after becoming Chief Secretary to the Treasury, when it emerged he had claimed £56,000 in expenses paid to his partner, Jamie Lundie – in breach of Commons rules.
The MP for Yeovil was suspended from Parliament for seven days last year after the Standards and Privileges Committee criticised him for a "series of serious breaches of the rules over a considerable period of time".
When he quit, the MP said his motivation was to hide the fact that he was in a gay relationship. At the time, friends said his elderly parents, both Catholics, did not know that he was gay.
Tony Laws, in an interview with the Daily Mail yesterday, said: "I was embarrassed my son had been caught taking money he was not entitled to. I think David was damn lucky that further action wasn't taken against him, as I know some MPs went to prison.
"I'm pleased for him, but I think he has gone back too soon. He should have waited until after the general election to let his constituents deliver their verdict."
Tony Laws, a retired City banker of Axminster, Devon, now divorced, did not reveal why he has not spoken to his son for 15 years. The father said he was angry that friends of Mr Laws had suggested he was an only child, when he has an adopted brother and sister.
"There was no row, no major fallout, I just think David lost interest in me as his dad," said Tony.
The 76-year-old said: "When he resigned from the Cabinet, he publicly acknowledged his sexuality. It came as no surprise to me."
David Laws declined to comment.