Last month the High Court said that the wording used in charging a man with failing to take a breathalyser test had been 'duplicitous'. This form of words has been used by prosecutors since 1967, since when between 125,000 and 200,000 motorists have been convicted, according to Sean Sexton, the Liverpool solicitor who spotted the loophole.
CPS lawyers hope the courts will only permit challenges by people convicted within the past 28 days. If all those charged since 1967 can appeal, the cost to the Treasury would run to millions.
In the test case, Terry Corkoran, 43, of Liverpool, was charged in the standard way with 'failing without reasonable cause to provide a specimen of breath for analysis in the course of an investigation under section four or five of the Road Traffic Act'.
Mr Corkoran challenged the prosecution on the basis that the charge sheet failed to specify which section was relevant, that he was driving a car, or was in charge of it.
Mr Corkoran, who said he had not been driving the car, persuaded magistrates and then the High Court that he had been charged with two separate offences on the same sheet, violating the rule against duplicity.
The CPS was refused leave to appeal but could have petitioned the House of Lords within 14 days. It has failed to do so, effectively conceding the case.
Many of the convicted motorists were fined and some lost their jobs, opening the way for compensation claims.