A staggering 33 sat-navs have been stolen from vehicles since the beginning of the month – more than one a day.

And there have been also been incidents of mobile phones and other valuables being swiped by thieves after careless drivers left them on display.

The majority of victims have been visitors to Peterborough, unaware that city thieves target parked cars.

Now police are urging drivers to ensure they take all valuables with them to remove the temptation of a smash and grab theft.

Community safety officer at Bridge Street Police Station Carol Aston said: "It seems people leave their vehicle secure but with valuables left on display and are shocked when they return to see a smashed window and items gone.

"The bulk of the victims are people from out of Peterborough coming into the city. It seems they think they can leave stuff on display then return to their vehicles to find the windscreen smashed and the valuables gone. It really is a reality check. Motorists must be more responsible and leave nothing on view that might tempt someone to break in. People shouldn't think, 'It won't happen to me', or 'I'm only going to leave it for a minute'. It takes seconds to smash a window and grab a sat-nav device and we know thieves are operating in the city.

"Crime is really going down but people are making it easy for the thieves."

In 2006 it was revealed that the city was the hot spot of sat-nav thieves in Cambridgeshire.

In the first four months of that year a shocking 144 of the 188 thefts recorded in the county took place in Peterborough.

Since then police have been cracking down on car thieves including setting up "trap cars" to catch thieves red-handed.

And in September police launched a fresh campaign urging motorists not to leave valuables on display.

In an ET investigation, a reporter and two police community support officers spotted 12 vehicles with valuables on display parked in Broadway, in the city centre, and the regional pool car park, off Bishop's Road. Many had left sat-nav cradles stuck to the windscreen advertising the fact there was likely to be a sat-nav system stored in the glove compartment.

Others left bags on the seats and one even left a prescription on the dash board for all to see. Another had left a set of golf clubs on the back seat.

All the vehicle owners were sent letters warning them about the risks of leaving valuables on show.

The police's community safety team will be in the Focus store's car park, off Lincoln Road, Walton, Peterborough, promoting crime-fighting initiatives such as Immobilise and SmartWater, from 10am to 2pm on Saturday.