An official review is expected to recommend cutting the legal limit from 80mg of alcohol per 100ml of blood to 50mg. It has been speculated a 20mg limit might be set for novice, lorry and bus drivers.
The Conservatives have said they would not change the limit if they came to power at the general election.
Any change is unlikely to take place before the next election as a 12-week consultation period is required. The changes would bring England and Wales into line with the rest of Europe.