The man was arrested on alleged firearms offences following a car chase. He had earlier been spotted acting suspiciously by officers in West Ruislip.
A suspect package seen being left by the man close to the South Ruislip Tube station was destroyed by the bomb squad in a controlled explosion. It was later found to have been an empty box.
Police last night refused to say whether they were questioning the man about more than 34 bombings over the past four years which have reputedly been the handiwork of the Mardi Gra bomber. However, sources suggested last night they had not captured the man responsible for attacks on homes, branches of Barclays bank and Sainsbury's supermarkets with bombs made from shotgun cartridges and timing devices.
Last night there were reports that undercover officers from Scotland Yard's Flying Squad had been carrying out a complex surveillance operation for the past six months and that the man had been arrested as part of that. Police sources suggested, however, that it was more likely that the Sainsbury's store at Ruislip - scene of a Mardi Gra attack in November 1997 - had been the subject of surveillance.
A spokeswoman for the Metropolitan Police night said the man had been chased by officers when he made off in a car. "The car was stopped a short time later. In the car was found what was believed to be a firearm," she said.
The area was later sealed off when officers found a suspect package outside the supermarket.
No details have been released about the man, believed to be in his 40s, who was being questioned in a London police station.
"All we are saying is that the package proved to be non suspicious. It is not a Mardi Gra device," said a spokeswoman.
The Mardi Gra bomber - so named because his early bombs were sent in video boxes bearing the words "Welcome to the Mardi Gra experience" - has been active in the London area since 1994.Reuse content