Former Liberal Democrat leader Charles Kennedy has been "spoken to" by police for smoking on a train.
Mr Kennedy was ousted as Lib Dem leader in January 2006
Police said a man had been advised of the no smoking policy on the 1105 BST Paddington to Plymouth train earlier.
They were told he was smoking on board and "refusing to stop", thinking it was fine to smoke out of the window.
Mr Kennedy, who was ousted as Lib Dem leader in January 2006 after admitting to a drink problem, has long tried to quit smoking.
The train manager on the First Great Western train called the British Transport Police after Mr Kennedy was discovered smoking on board, the BBC understands.
It is thought there was some sort of confrontation between the Lib Dem MP and train staff.
The train was met on arrival by the police where Mr Kennedy was spoken to about his behaviour. He was not arrested.
British Transport Police, who refused to confirm the identity of the man on the Plymouth train, said "the matter was resolved informally".
A spokesman for the Liberal Democrats refused to comment, saying it was a private matter.
Mr Kennedy backed the England-wide ban on smoking in enclosed public places last year, but during the 2001 General Election campaign he was known to allow people to light up on his plane.
Despite a New Year's resolution to quit the habit for 2005, he admitted he was still smoking the following April, but said it had come down "drastically".
Speaking before the birth of his son, he said: "I am determined that it is going to be phased out altogether - particularly since the arrival of the new one."
It appears Mr Kennedy is not the only MP flouting no smoking policies.
On Thursday the House of Commons was told MPs were not obeying the new smoking ban.
Although not illegal in the Palace of Westminster, both Houses of Parliament agreed to restrict smoking to four designated outside areas, although those caught smoking will not face financial penalties.
During a Commons debate on Thursday, Labour MP Betty Williams offered to show Leader of the House Harriet Harman where people were smoking - to be met with cries of "division toilets" from other MPs.