A male streaker leapt onto the stage while British Liberal Democrat leader Charles Kennedy was making a speech.
The man had been wearing Velcro clothes which he took off as he approached the stage at the Liberal Democrat rally in South London.
He was left sporting a party hat and writing on his chest and backside.
After the interruption Mr Kennedy quoted US president Harry S Truman, saying: "If you can't stand the heat, don't go in the kitchen."
He then said Nye Bevan might be more appropriate, and quoted: "Don't go naked into the conference chamber."
The streaker had the words "General Erection" written on his chest and the letters V, T and E written on his buttocks.
Mr Kennedy took a small step backwards when the streaker suddenly appeared from stage left just a few yards from him.
But as he was bundled off, a relaxed Mr Kennedy joked: "We're the Liberal Party, we can put up with that."
A 36-year-old man from Liverpool was arrested following the incident and taken to Fulham Police Station.
A Scotland Yard spokesman said: "A man was detained by security staff and arrested by police for a breach of the peace."