The Home Office has said it is satisfied with the accuracy of a breathalyser used by dozens of police forces in the UK - despite allegations that the device is faulty.

The Intoximeter EC/IR, which was introduced to police forces two years ago, has been used to secure thousands of drink-drive convictions.

But a national newspaper has revealed that tests carried out on the equipment by scientists at the St Bartholomew's and Royal London School of Medicine show results to be 6% to 8% too high.

Dr David Trafford and Professor Hugh Makin, of the department of clinical biochemistry at the college, spoke out after they conducted a series of tests involving both the Intoximeter EC/IR and another Home-Office-approved breathalyser, the Lion 6000.

But the Home Office has said it is satisfied the Intoximeter is accurate.

'Extremely worrying'

Dr Trafford told the Daily Mail that it appeared the machines had never been tested on human volunteers who had consumed alcohol.

He said: "It was just by chance we did the experiments.

"We didn't set out to look at comparisons, we simply had both machines in the lab and compared the results out of interest.

"We were very surprised to find the Intoximeter EC/IR gave remarkably higher readings than the Lion.

"For example, if an average man has drunk two pints, close to the legal limit, the machine gives a reading as if they were over the limit. It is extremely worrying."

A spokesperson for the Home Office said: "We are aware of the allegations but the Forensic Science Service has carried out tests on these instruments and we remain satisfied with their accuracy."