The TV watchdog has upheld complaints that Jeremy Paxman was "offensive and insulting" when he questioned the Liberal Democrat leader on his drinking habits

While questions on the issue of Charles Kennedy's personal habits and decision to get married were legitimate, the Broadcasting Standards Commission ruled that Paxman's persistent probing had "exceeded acceptable boundaries".

The Newsnight presenter has already apologised for the interview, which saw him asking whether Kennedy sat alone drinking "a bottle of whisky late at night".

The Lib Dem leader said he drank "moderately and socially".

He was also asked whether his then fiance Sarah Gurling kept him on the straight and narrow.

Two viewers had complained about the interview, saying they found it "offensive and insulting".

The BBC claimed that the issue of Kennedy's drinking arose from comments made by politicians during research for the interview.

It defended questions on Kennedy's marriage, saying it had gone no further than enquiring why the Lib Dem chief was opting for marriage.

The BSC conceded that "as a leader of a sizeable parliamentary party with aspirations to government" Kennedy was always likely to be subject to rigorous questioning on his personal life.

"However, in the panel's view the presenter's prolonged questioning of Mr Kennedy in relation to personal matters had been overly intrusive in nature and tone and had exceeded acceptable boundaries for broadcast," it added.

Following a row over the interview, Paxman said he had "always found Charles Kennedy an affable chap".

"I am sorry if any offence has been caused. Maybe there was one question too many on drink," he conceded.

Speaking at the time, the Lib Dem leader brushed off speculation about his drinking habits as the "kind of thing that goes around the hothouse of Westminster".