MP Eric Joyce has been arrested for allegedly fighting with two teenagers in a London shop.
The 54-year-old was questioned on suspicion of causing actual bodily harm and bailed to appear at a later date.
However, in his online blog, the Falkirk MP claims he detained one of the youths after the shop had been damaged and the teenager subsequently alleged assault.
A Metropolitan Police spokesman said: “Police in Camden were called to a convenience store in Chalk Farm Parade, Adelaide Road, NW3 at 2142hrs on Friday, October 17 following reports of a fight.
“Upon arrival officers found a man and two teenage boys involved in an altercation.
“A 54-year-old man was subsequently arrested on suspicion of ABH.
“A 14-year-old boy was also arrested at the scene for possession of cannabis.
“Both were taken to a central London police station for questioning and have since been bailed to a date in early December pending further enquiries. Neither required medical treatment.
“Police in Camden are investigating and enquires continue.”
But Mr Joyce said: “I detained a youth in a shop in London. Damage had been done to the store. I asked the shopkeeper to call the police, and when officers arrived they arrested the youth and informed me that drugs had been recovered from the scene.
“The officers also informed me that the youth had immediately made a complaint that I had assaulted him by detaining him. I was questioned by the police and told that because of my identity the Crown Prosection Service and the Metropolitan Police press office would be informed of the incident.
“I understand the Metropolitan Police has now made the matter public. I will make no further comment for now, other than to say a) that no alcohol was involved and b) I am not in the habit of summoning the police if I felt that I am in the wrong.”
Officers told Commons Speaker John Bercrow of the arrest and MPs were informed of the matter in a circular last week.
Mr Joyce quit Labour in 2012 after headbutting a Tory MP in a House of Commons bar brawl.
Earlier this year he was fined £1500 for swearing at baggage handlers and police at Edinburgh airport.