Do-it-yourself breath test machines in car parks will tell drivers if they're over the limit

Drivers blow into a plastic pipe until prompted to stop and seconds later a reading flashes on a screen, telling them whether they can legally drive.

The Alcolizer machines use the same technology as police breathalysers.

But a spokesman for the Association of Chief Police Officers told motorists not to rely on the machines and issued a blanket warning not to drink and drive.

He said: "We see a lot of these gimmicks. It is difficult to know how accurate they are. Our message would be: 'Do not drink and get behind the wheel. Full stop.'"

A spokesman for Risk Shifters, the company distributing the breathalysers, said: "The whole point of having a breathalyser available in a car park is not to encourage drink-driving. It is to provide users with information.

"It does not give them a guarantee. It does not provide them with a defence if they are then stopped by the police and fail a test.

"The body absorbs alcohol at a regular rate and your alcohol level can rise for some time after you have had a drink.

"If you are close to the legal limit when you use the Alcolizer you should wait a few minutes and test yourself again."

Four Alcolizers, costing £5,000 each, have been installed in car parks run by Q-Park. One in Leeds is free of charge and three in Glasgow cost £1 a time. Each user is provided with a clean pipe to blow through.

Q-Park has bought three more machines which it plans to install at other locations, and Risk Shifters is also in talks with other car park operators.

The Australian maker, Alcolizer Technology, also produces breathalysers for police in Australia and China.

Frank Soodeen, of the charity Alcohol Concern, backed the machines. He said: "This sounds like a good idea. We would welcome any device which allows drivers to accurately gauge the amount they have drunk.

"It encourages motorists to act responsibly. We support that."

Road safety charity Brake cautiously welcomed the Alcolizer but warned drivers not to rely on it.

Spokeswoman Dianne Ferreira said: "In principle it is good. It makes people think about how much they have drunk.

"But there is a danger motorists will try to drink to the limit and then use the machine to check they are OK. We urge caution."