David Gates found himself being questioned under the Terrorism Act after he spotted the BMW in the middle of the box reserved for buses, and decided to capture the image on his phone – apparently falling foul of the anti-terror law in the process.

Mr Gates was then questioned by two officers who asked why he had snapped the picture of their vehicle, and they told him he was being quizzed under the Terrorism Act 2000 because the picture could pose a security risk.

They also said this law gave them the right to use stop-and-search powers.

Mr Gates, 42, saw the car in New Road, Copnor, Portsmouth, while the officers were knocking at a door.

He said: 'I explained I'd taken the picture as their car was parked illegally, and taking a photograph in public was not illegal.

'I told them I thought using the Terrorism Act and suspecting me of being a terrorist was ridiculous.'

Mr Gates, an account manager, of St Andrew's Road, Southsea, said he co-operated with the officers and gave his details, which were checked. He was told the record of the incident would be kept on file for a year.

Mike Hancock, the Lib Dem MP for Portsmouth South, said: 'The whole thing is quite bizarre. I don't have a problem with them parking at the bus stop, but I do have a problem with them using this legislation for something trivial like this and keeping it for a year.

'If this was used in Portsmouth 50 times in a year, the statistics would make the city look like a hotbed of terrorism.'

Superintendent Neil Sherrington, the deputy commander for Portsmouth police, said: 'Officers are given powers under the Terrorism Act to stop and search.

'The act states that "this power can only be used for the purposes of searching for articles of a kind which could be used in connection with terrorism, and may be exercised whether or not the constable has grounds for suspecting the presence of articles of that kind".'

He added: 'It is therefore reasonable for the officer in this case to have made reference to the act and been suspicious about why the photograph of the vehicle had been taken.'

He said the officers were dealing with a domestic incident in New Road, and could find nowhere else to park.