Dead tired or dead drunk? Fatigue kills - Booze: you lose

The prize for the worst driving still goes to the drunk. By 11.40pm, Peter had consumed 12 units - more than double the legal limit for driving.

Apart from giggling like a schoolgirl, other ill effects included a 49% decline in his ability to maintain a steady distance from the car in front, and his driving within the lane suffered by 42%.

His reaction time was 43% slower than when he was only just over the limit.

He spent a long period driving at 70mph in third gear and crawled round the 60mph bends at 45mph in a bid to stop swerving around in the lane.

This slower driving is unusual in drunk drivers, Professor Parkes explains. 'Normally you'd expect a drunk to drive faster and more aggressively.'