Boris Johnson has apologised for giving his wife a "backie" on a bicycle, claiming he was "unaware" he was breaking the law.
The mayor of London was criticised by the national cycling charity CTC for pedalling his barrister wife Marina Wheeler through the city late on Thursday night on a bicycle designed for one person. The charity said he "should have known better".
But Mr Johnson's official spokesman said the mayor was "unaware that he was apparently in contravention of the Road and Traffic Act".
"The mayor wishes to apologise for offering his wife a short lived lift on the back of his bike!
"He wasn't intending to ride all the way home from North Kensington to North London with Marina on the back, rather he was attempting to transport his wife to a main road, from where they hailed a black cab for her."
The spokesman added: "As everyone knows, the mayor is a huge supporter of cycling, and an even bigger fan of the black cab trade, hence his desire to combine the two!"
Sam Jones, from CTC, said: "We wouldn't encourage other cyclists to carry passengers in such a fashion. We would never encourage cyclists to break the law."
Mr Johnson's romantic gesture could land him in trouble with the police as giving a backie is illegal under Section 24 of the Road and Traffic Act (1998) and offenders can be fined up to £200.
The act states: "Not more than one person may be carried on a road on a bicycle not propelled by mechanical power unless it is constructed or adapted for the carriage of more than one person."
Mr Johnson was caught on camera by passengers in a passing car as the couple cycled along Barlby Road in North Kensington.
The footage, obtained by The Sun newspaper, shows Ms Wheeler sitting on the saddle, without a helmet, clutching onto her handbag as Boris stands on the pedals.
After the passengers informed the mayor that he was breaking the law, Mr Johnson stepped off the bike and said "night, night" to them.
They can be heard in the video asking the mayor: "Mate, you all right? Saddling that's a good one eh?"
Another says: "You're not allowed to do that mate."
The mayor, whose responsibilities include London transport, has had the city's bike-sharing scheme colloquially named after him.