Seven more held in Britain for terror offences
Police said one man from West Yorkshire and six from West Midlands are being questioned on suspicion of the commission, preparation or instigation of acts of terrorism, The Sun reported.
Police said the contents of the car were undergoing forensic analysis and the suspects' homes had been searched.
The arrests followed a routine stop of a vehicle by police on a motorway in South Yorkshire. The car was impounded on suspicion of having no insurance, a police spokesman said.
"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," he said.