[Neil]

Have a read of this Drink-Driving Guidelines

Here is a bit of it

To ensure you run no risk of being "over the limit":

Immediately before driving:
- men should consume no more than 4 units, women no more than 3

When drinking the night before driving:
- men should consume no more than 10 units, women no more than 7. (This assumes that no alcohol is consumed after 11.30 pm, and that driving does not take place before 8 am the following morning)

This applies to people of average weight (around 12-13 st for men, 9-10 st for women). If you are particularly small, these figures should be reduced accordingly. But if you are particularly big, it is no guarantee that they can be increased. The figures are lower for women not only because they are usually lighter than men, but also because their metabolism is different.

If you drink more than this, it will not guarantee that you will exceed 80 mg, as the rate of absorption of alcohol is so unpredictable. But even with one unit more you will be running a tangible risk. The above figures are the maximum you can consume without any significant risk of exceeding the legal limit, and also without resulting in any significant increase in accident risk.

It is also important to remember that a half pint of beer or a glass of wine can contain considerably more than one unit. Given that most pubs serve draught beer 5 to 10% under measure, it is fairly safe to assume a half of any beer up to around 4% represents one unit. But, any higher than that, and you have to make adjustments. A pint of 5% beer is almost three units, and even one and a half pints may not quite be safe.

In 1967, very little beer was available above 4% ABV. Now, it is widespread, and in some pubs it can be be difficult to find beer below that strength. In particular, the 33 cl bottles of "designer lagers" that are so popular are usually between 5% and 5.5% ABV, meaning that each contains almost two units, and any more than two could take a driver above 80 mg.

The risks with wine are even greater. Only the very lightest German wines have an ABV as low as 8%, and many pubs and restaurants serve wine in 175 ml or even 225 ml glasses, rather than 125 ml. A 175 ml glass of wine of 12% ABV, which is fairly typical, represents two units. Two such glasses could put a smallish woman over the limit, whereas two pints of bitter would not do so for an average-sized man. An increasing number of pubs are now also serving spirits in 35 mg measures, containing 1.4 units, rather than 25 mg which is exactly one unit.