Nick Clegg has described the “surreal” night when he drunkenly set fire to a cacti collection in Germany as a teenager.
The Liberal Democrat leader admitted the arson in 1983 on Radio 4’s Today programme.
“I have not been convicted of arson at any time in my life but I did commit a bad thing when I was a teenager,” he said.
“It’s such an odd story, I set light to some cacti. It’s such a surreal thing to say.
“In Europe no less, an act of rare anti-Europeanism.”
When asked if he was drinking he said he “behaved badly” like many teenagers.
He added: “I was told off. I had to do penance, I had to do a form of community service.
“I was digging up flowerbeds in a suburb of Munich.
“I’m not proud of it, it’s terrible. I don’t know why we’re talking about this.”
The Deputy Prime Minister was questioned over his prickly past by John Humphrys after Nick Griffin, leader of the BNP, raised the allegation on Wednesday’s programme.
His misdemeanour was originally revealed in 2007 when Mr Clegg was speaking at a Liberal Democrat fringe meeting.
He was 16 at the time and was visiting Munich on a trip with Westminster School.
Mr Clegg was sent to stay at with the family of a professor, who was also a collector of rare cacti.
The number of plants damaged has been disputed but he described vandalising them with a lighter.
His admission deviated from the subject of Britain’s relationship with the EU on the Today programme.
Mr Clegg sparked controversy by calling Eurosceptics “deeply unpatriotic”.
He argued that advocating continued membership of the EU was a “pro-British position”.
“I don't see how you can be pro British jobs, pro putting money in people's pockets, pro giving the police the power to go after criminals across borders unless you're pro us being a committed member of the EU,” he said.
"[Leaving] would be damaging to Britain and would therefore be an unpatriotic thing to do to say that joblessness, unemployment - which is one of the most immediate consequences of our withdrawal from the EU - is a price worth paying.
“I think that's deeply unpatriotic, and very unfair on the people who would lose jobs.”