POLICE are cracking down on illegal number plates because of concerns they may be interfering with anti-terrorist investigations.

PC Peter Hare from the Amersham Traffic Unit is involved in the blitz on number plates and sent out 200 letters before Christmas to warn owners to sort them out or suffer the penalties.

He said that customised, personalised and altered plates can cause big problems for the police, even interfering with anti-terrorist investigations.

He added: "People messing with their number plates is a problem, especially the squiggly funny-shaped ones."

PC Hare said that automatic number plate readers used by the police can scan number plates and detect if it is stolen, or help to identify whether it is being used for "serious criminal activities".

However, a mother-of-four, who asked to be anonymous, had been on the school run in January when she was stopped because the characters on her number plate were too far apart.

She said: "When I saw the blue lights, I thought one of the children had tumbled out of the back of the car or he was going to tell me my husband had been in a crash."

But as she pulled over in Amersham Road, Beaconsfield, the officer told her to get out of the car.

As she approached the rear of the vehicle she said he told her: "Your number plate is 11mm out."

She added: "The way I was stopped I thought I must have looked like Ronnie Biggs or something. I thought he was some kind of loony telling me the number plates were 11mm out."

However, PC Hare said that messing around with number plates was becoming a serious problem. He added: "I have even seen someone driving around with a plate that read 'Barbie'."