Seven men have been arrested on suspicion of terrorism after police found guns and other weapons hidden in a car that was impounded for having no insurance.
One man from West Yorkshire and six from the West Midlands are being questioned on suspicion of the commission, preparation or instigation of acts of terrorism following a series of arrests this week.
West Midlands officers had impounded the uninsured car, only to find two guns, some ammunition and other offensive weapons hidden inside.
A spokesman said: "The arrests followed a routine stop of a vehicle by police on the M1 motorway in South Yorkshire on Saturday (June 30). The car was impounded on suspicion of having no insurance.
"Firearms, offensive weapons and other material were later found hidden inside, prompting police to take action to trace and arrest the driver, passenger and others suspected of being involved."
The car was stopped between junctions 33 and 34 of the southbound M1.
This follows a separate counter-terror swoop in London on Thursday, which saw six arrests in Stratford, east London and Ealing, west London. A former police community support officer and Muslim convert Richard Dart, 29, were said to have been among those held.
West Midlands Police said that in the latest arrests, three men aged 23, 26 and 27 from Sparkhill, Birmingham, were held on Tuesday morning.
Three more suspects, a 22-year-old from Alum Rock, Birmingham, a 24-year-old from the Moseley area of the city, and a 22-year-old from Smethwick, West Midlands, were arrested on Wednesday evening. A 43-year-old man from Kirklees, West Yorkshire, was detained in Ravensthorpe, Dewsbury, on Thursday.
Detectives have been given extra time to question the three men arrested on Tuesday, after the initial 48-hour detention period ran out. They now have until next Tuesday morning to charge or release the men, or apply for a further warrant. All seven men are being held in the West Midlands.