Mr Clegg said everyone had 'blemishes' in their past

As a 16-year-old exchange student in Munich, he was given community service after setting fire to a rare collection of cacti in a "drunken prank".

Mr Clegg - whose leadership ambitions have been the talk of the party's conference in Brighton - made his admission at a fringe meeting.

He later told the BBC he was "not proud" of the incident, which saw him digging gardens as a punishment.

When he returned to England, he was ordered to spend the holidays - and a lot of money - finding the cacti he had destroyed and sending them on to the German professor whose collection he had ruined.

Speaking to BBC2's Daily Politics Conference Special, Mr Clegg said: I did some damage to some plants. I am not proud of it. I think we all have blemishes in our past."