New laws to make it more difficult to dispose of stolen cars are set to come into force after a government bill received royal assent on Tuesday.

The measures, contained in the Vehicles Crime Act, will see the motor salvage industry becoming subject to stringent regulation, to stop backstreet operators changing the identity of stolen cars - a practice known in the used car trade as "ringing".

The supply of number plates is also to be regulated, under measures contained in the act which also introduced new rules which must be met before a car can be "written off".

The bill also extends the sentences which can be given to those found guilty of car theft.

Speeding drivers will also be hit by the new legislation, which will use the cash generated through fines to invest in more speed cameras.

Welcoming the new act, the home secretary, Jack Straw said it would make buying a used car less risky in future.

"Motorists need to feel confident when buying a second-hand car that it is the vehicle the seller claims it is. We estimate that up 78,000 vehicles a year have been used for 'ringing' or broken up for parts which can be sold on to unsuspecting motorists."He said attacking car crime could also reduce other criminal activity.

"Cars are stolen for many reasons, including as a means of committing serious offences using vehicles which cannot be traced. This can include terrorism, armed robbery and burglars using vehicles to transport stolen goods. The Act means that it will no longer be possible to buy a vehicle at a salvage yard or new number plates without proper identification or checks," Straw said.