Morning-after motoring: Is it safe to drive with a hangover?

Does a good night's sleep mean it's safe to get behind the wheel? Simon Usborne mixes a real hangover with a virtual car to find out

According to the online alcohol consumption calculator, www.RUpissed.com I am, indeed, pissed. It's been more than eight hours since I drank the last of six (or was it seven?) pints of strong lager (and a shot of sambuca), yet the website tells me almost half the alcohol I consumed will still be in my system. Since then, I've slept and downed litres of water, but at eight o'clock the morning after the night before, I'm unsteady on my feet and feel rougher than hell.

The website tells me I must have have a blood alcohol content of about 60 milligrams. The legal maximum in the UK is 80mg, so I suppose that means it's safe for me to drive. But is it?

The first few miles seem OK. I steer a Jaguar S-Type through city streets without incident, stopping at the lights and weaving only slightly as I negotiate a bend. It's a clear, sunny morning and the roads are quiet. As memories of the last night's drinks binge begin to surface somewhere behind the headache pounding my skull, I feel like I'm driving pretty well. And whatever - I'm legal.

And then it happens. I spot the people carrier stationary in the slow lane of a dual carriageway but, as I overtake it, I don't slow down. And when the car pulls out as I pass, I do not brake soon enough. Hitting the car at about 30mph, I screw up my face and instinctively duck my head as my windscreen shatters.

This time, thank God, I'm not driving a real car. I'm sitting in a simulator at Brunel University in Middlesex. A team of scientists, in partnership with the insurance firm RSA, have just carried out a study into how well (or badly) we drive the day after a party. A virtual city is projected on to screens in front of the Jaguar and the car's controls are hooked up to a computer that records every inch of a seven-minute drive.

The results are disturbing. On average, the student participants, all of whom were under the legal limit, drove almost 10 per cent faster and committed twice as many traffic violations after a night out than they did with no drink in their system. After my turn, during which I had to pull over in the virtual world to throw up in the real one, Dr Stewart Birrell gives me my results. They're not good. For almost 20 per cent of my journey I've been driving over the speed limit and I've committed seven driving violations.

David, the photographer who's with me, has been watching my drive. Afterwards, he tells me a Dalmatian had walked out from behind a car on the other side of the road. "What Dalmation?" I ask. "If anything, I think you accelerated," he replies.

Back at the office, struggling to gear my addled brain towards writing this piece, I call an expert to find out why I drove so badly when, technically, it was legal for me to get behind the wheel. Professor Vivienne Nathanson is head of science and ethics at the British Medical Association (BMA), which recently published the report Alcohol Misuse: Tackling the UK Epidemic.

She's horrified that I consumed more than 18 units last night – some way above the Government's daily guideline of three to four units for men (don't tut like that; it was a party!).

"Did anyone tell you that that's a toxic level of alcohol?," she asks. My stomach did, I feel like saying.

"It fills me with dread to think that people are getting into cars in that condition," she continues. "I think we overestimate the speed at which we get rid of alcohol. Because you're less drunk than you were, it's very easy to make the mistake of thinking you're fit to drive."

Nathanson says it's no wonder I was a risk on the road. "If you're dehydrated and your brain's short on fluid, then it will slow down. Even with 20mg of alcohol in your system [that's one quarter of the legal limit], your ability to concentrate, make choices and react is impaired. Combined with the toxicity of the alcohol and tiredness, it makes driving unsafe."

The BMA's research suggests drivers with a blood alcohol content between 50mg and the legal limit of 80mg are a hidden cause of crashes. Some estimates suggest "legal drink driving" causes 80 road deaths a year in England. That would be on top of the official 460 deaths (16 per cent of all road deaths) caused by drivers over the legal limit last year in the UK.

A cultural shift in recent years has brought drink-driving deaths down – there was an 18 per cent decrease last year – but, as the party season gathers pace, awareness of the effects of a bad hangover appears to be lagging behind. The BMA is campaigning for a cut in the legal limit from 80mg to 50mg, which would bring the UK in line with Europe (only Ireland, Malta and Cyprus have limits as high as ours). "[The Government] claims to have an open mind and that it wants to see the evidence," Nathanson says. "The evidence is there and it's clear."

I've learnt two things by doing the test: that I can't hold my drink, and that drink-driving in this country needs to be redefined. Chastened, I'm left wondering what would have happened had that people carrier been a real one with a real family inside.