Police say any valuables left on display are easily targeted

Police said there had been a "huge leap" in the number of thefts as drivers ignored repeated warnings not to leave the devices on show.

Det Supt John Parr said more than 300 systems had been stolen from vehicles in Sheffield this year, compared with seven during the same period in 2005.

"If you leave your sat nav device on display you will get it stolen."

So far this year the overall number of thefts from a vehicle in Sheffield has risen by 48%, from 4,245 offences to 8,165.

South Yorkshire Police said it was trying to combat the problem, by leaving bogus vehicles parked in crime hot spots, and several arrests had been made.