Motorists are being advised not to rely on personal breathalysers during the Christmas drink and drug campaign.

Tests carried out by Dorset County Council’s Trading Standards officers revealed that drivers relying on shop-bought breathalysers would put both themselves and other road users at risk.

Out of 14 devices tested, nine indicated that the user was still safe to drive when the legal drink-drive limit was actually exceeded.

Officers also found false claims of links to the police on four of the devices which were bought over the internet.

Inspector Matt Butler, of Dorset Police’s Traffic Unit, said: “This survey revealed that home breathalyser kits can be unreliable so we are urging people not to use them.

“Research has shown that just one drink can impair someone’s ability to drive.

“Our message is very clear – if you are going to drive, don’t drink any alcohol at all.”

Ivan Hancock, Trading Standards service manager for Dorset County Council, said: “Our research shows that there is a wide variety of cheap breathalyser kits available for sale on the internet.

“Our tests have highlighted that the majority of these are unreliable and may give a dangerously false sense of security. Drivers would be extremely foolish to rely on the readings they get from one of these cheap devices.

“Use your head – just don’t drink and drive.”

This year’s campaign has received the backing of Margaret Waterland, whose husband David, 68, of Wareham, was killed by a drink-driver in Milborne St Andrew near Blandford on May 15, 2013. Stewart Rosoman, 51, was jailed for six years in November 2014 for the offence.

Margaret said: “Drink driving is simply not worth it. It is not only innocent lives you destroy but you also ruin your own family’s lives – they suffer too.”

As in previous years, anyone charged with a drink or drug drive-related offence during the campaign will have their names and court appearance details released to the media. Custody images of those convicted could also be released to the media.

To date seven people have been charged with a drink or drug driving–related offence.

Call 101, or 999 immediately, if you suspect someone is drink or drug driving. Calls can be made to Crimestoppers anonymously on 0800 555111.