Motorists convicted of drink driving are to be forced to have "alcolocks" installed to regain their licences.

The special locks require the driver to blow into a mini-breathalyser and, if he is over the limit, prevent him from switching on the engine.

The measures, which will be outlined in a Road Safety Bill, are intended to tackle a hard core of motorists who continue to drink and drive.

The government yesterday ruled out introducing random breath testing.

David Jamieson, the transport minister, told the Commons transport committee that he preferred "targeted" testing.

"I don't see why we should be upsetting vast numbers of people who are going about their business in the normal way," he said.