Road safety campaigner Clive Matthew-Wilson, who also edits car review website, dogandlemon.com, was shocked to learn the practice was legal and called for a law change.
"It's completely crazy. I just can't believe our lawmakers are that stupid," he said. "It's like saying you're allowed to drive carrying a handgun as long as you're not shooting anyone.
"One tends to follow the other. If you're drinking while driving, then it's highly likely that it's going to cause serious road safety problems."
Assistant Commissioner Road Policing Dave Cliff highlighted Ministry of Transport figures that showed drinking and driving killed 1463 people and injured 24,789 others in road crashes between 2000 and 2011.
Anyone found over the legal limit while behind the wheel would face the "full pressure of our resources to remove them from the road". Vehicle owners may also find that their insurance does not cover them for alcohol consumption behind the wheel. Mr Cliff noted that police do not make the law.
A spokesman for the Transport Agency said: "Consuming any amount of alcohol impairs your ability to drive."
Nigel Hampton, QC, said motorists may not be breaking the law by drinking a beer while driving, but police could have "very good cause" to pull them over.
Read more: Teen attempts to fool breath test with deodorant
Send your story, photos or video here.