Test yourself the morning after

BREATHALYSERS don’t measure the amount of alcohol in the blood directly — they measure the electrical resistance created by alcohol in exhaled air to calculate the blood alcohol level.

This is why it is unwise to rely on a DIY breath test to check you’re OK to drive home after the pub, warns Tony Moss, professor of addictive behaviour science at London South Bank University.

‘Your blood alcohol level can carry on rising for a good hour or even two after you stop drinking, so midway through the drive home you could be over the limit.’

He suggests using a DIY breathalyser before you drive the following morning — many motorists stopped by the police the morning after find they are over the limit.