Motorists feel more confident driving after one double drink than two singles, even though they contain the same amount of alcohol, research has found.

       A third (33 per cent) of motorists said they would feel more comfortable driving after one double spirit with a mixer compared with 19 per cent who chose two single spirits – even though they contain the same number of units.

       The survey of 2,000 adults for Churchill Motor Insurance showed that overall up to 34 per cent of motorists said they would have drinks containing between two and four units in the belief that they would not break the law.

       In England, Wales and Northern Ireland, the alcohol limit is 35 microgrammes per 100 millilitres of breath, but 22 microgrammes per 100 millilitres in Scotland.

       It is generally estimated that four units (roughly two pints of normal strength beer) would put a man over the limit, compared with three units for women.

       'If you are going to drink, don't drive'

       Jack Cousens, head of roads policy at the AA, said: “It's the 'one drink' mentality. Our advice is simple: if you are going to drink, don't drive. And if you are going to drive, don't drink.

       "That is our basic call to arms because people do not have an understanding of how much a unit is or how many units they are allowed. Everyone's body is different and handles alcohol differently. You cannot say that everyone can have two pints and you are fine."

       The research also found 36 per cent of British adults who have driven after drinking alcohol said they had done so with children in the car.

       Although men were more likely to do so than women, with 39 per cent admitting having a child in the car, there were still 32 per cent of women who said they had.

       The research was timed for the August holiday season when drink driving arrests are on a par with Christmas at nearly 250 a day.