Oxford's criminals are stealing motorists' number plates to avoid being caught by the plethora of 'Big Brother' cameras now watching the city.

There has been a 25 per cent surge in licence plate thefts in the past 12 months in the city with one stolen almost every other day and police believe it is down to their own crime-fighting cameras.

Now they have launched a campaign offering motorists thousands of free 'one-way' screws to combat the thieves.

It appears to be an Oxford problem, 163 were stolen in the 12 months to April, compared with only a handful taken in nearby towns.

Nick Gilbert, of the Oxford crime reduction team, said the criminals were trying to dodge the police's own roadside automatic number plate cameras that spot suspicious cars, speed cameras, congestion charging cameras, private security cameras, and to steal petrol from gas stations.

It has seen innocent motorists then facing prosecution for 'bilking', filling up and driving off from petrol stations without paying, and other crimes.

Mr Gilbertof the crime reduction team, said: "People using vehicles for nefarious purposes don't want their movements known, so they take number plates from similar vehicles and use things like velcro. They can then use the cars for things like 'bilking'.

"Many people don't report number plate theft, and then they get a letter from the police or petrol station saying they drove off without paying for fuel, and it can get very heated.

"We've always had a few number plates going missing, but it has never been such a problem as it is now. But it's the plate thefts that don't get reported that we are worried about.

"Potentially, the cost could be a huge amount. If they are filling up at a petrol station every time, it could run into tens of thousands of pounds every year."

Plates are stolen and then taped, glued or velcroed over existing plates. They are removed when the crime is done.

"Some of them are very sophisticated. They come up with all sorts of things and we must be one step ahead," added Mr Gilbert.

Around 5,000 free screws are now being made available for motorists as police aim to fight the hidden crimewave.

The simple flat-head screws are easily attached, but cannot be unscrewed.

Mr Gilbert said: "Once the one-way screws are in place, the only way a number plate can be stolen is for it to be broken, and then it is useless."

Four screws per person, with simple fitting instructions, are available from front desks at Cowley and St Aldate police stations.