The M6 Toll motorway has been closed after armed counter-terrorism police stopped a coach in the West Midlands.
Sky's crime correspondent Martin Brunt said the passengers had been removed and the vehicle was being searched.
The Highways Agency confirmed that the motorway had been closed in both directions following a "police-led" incident.
The operation came just hours after a reportedly unrelated operation in which five men and a woman were arrested on suspicion of the commission, preparation or instigation of acts of terrorism.
The six suspects - aged between 18 and 30 - were arrested by armed police in pre-planned operation at locations across London and taken to a police station in the south-east of the capital where they remain in custody.
A 24-year-old man was tasered during his arrest at a house in east London but did not require hospital treatment, police said.
Brunt said: Scotland Yard's counter-terrorism unit had been watching these people for some time, perhaps several weeks.
"I am being told at the moment that there is no suggestion that whatever this plot was, and it was a plot to cause explosions or bombs of some description, the Olympic Games don't appear to have been the target."
He added that Jonathan Evans, the Director General of MI5, said in a speech a week ago "there are lots of plots going on, being discussed on the streets of Britain".
"He made it quite clear that there is continuing concern that there a lot of people who are thinking about, or plotting terrorist attacks in the UK. He also made the point that there is a new wave of British men that is travelling to terrorist training camps in the Middle East."
In a statement, the Metropolitan Police said: "Searches under the Terrorism Act 2000 are being carried out at eight residential premises in east, west and north London and one business premises in east London.
"Public safety remains our overriding concern."
More to follow...