Britain is experiencing a vodka boom that is worrying medical experts and increasing the violence that blights many town and city centres at the weekend.

Sales of vodka have risen by 40 per cent in five years and it now accounts for more than half of all white spirits drunk. Many young people in pubs and clubs, especially women, knock back large quantities of "ready-to-drink" vodka mixes such as Smirnoff Ice.

Experts have also noticed a rise in "pre-drinking", where young people consume large quantities of cheap vodka before their night out. Concern is rising that next month's shake-up of licensing laws - the biggest for 50 years - will encourage "post-drinking". Clubbers will be able to pick up cheap, own-label spirits from supermarkets and convenience stores at 4am and carry on drinking when they get home. A supermarket bottle costs £7 but contains 28 units of alcohol.

Some women say they prefer vodka because it has fewer calories and causes less severe hangovers than wine. Mixes mask the taste with sweet ingredients.

Professor Colin Drummond, a psychiatrist who treats alcoholics at St George's Hospital Medical School, London, said vodka was increasingly popular with young women, the group with the biggest increase in alcohol problems.

Many of his patients go through a "vodka stage" before moving on to even cheaper super-strong lager and cider. He said: "Some of my younger patients drink a bottle of wine or half a bottle of vodka before they go out so that they are primed for a night club."

Alcohol consumption in Britain has doubled since the 1960s. Ten times more young people are getting cirrhosis now than 30 years ago. Under the licensing law reforms, pubs, clubs, cafes, cinemas, off-licences and shops will be able to sell alcohol 24 hours a day. About 30 pubs have applied to open round-the-clock .

The Government hopes liberalisation of hours will encourage more sensible Continental-style drinking, where bars open later with fewer problems. But doctors say Britain already has a bad alcohol problem and extending the opportunity to drink will make it worse.

They say the British have an entrenched and profoundly different drinking culture to that of mainland Europe. They are also concerned at the £1bn a year spent on alcohol marketing.

"We don't know what the effects are going to be but every group - social workers, doctors, police or ambulance workers - think licensing reform will increase and not decrease the problem," said Professor Ian Gilmore, chairman of the Royal College of Physicians' alcohol committee.

"We are seeing people in their 20s and 30s with alcoholic liver disease that we would never have seen when I became a consultant 20 years ago. We are facing a time-bomb of alcoholic liver disease."

'The hangovers aren't so bad': Jane Oliver. Recruitment consultant. 25

By Kate Wiggans

When Jane Oliver celebrates her 25th birthday at a fancy-dress party tonight, guests won't be short of vodka. In preparation for a raucous night at her flat, in Tooting, south London, Jane and friends have spent £60 on drinks, mostly vodka.

"I drink vodka most weekends," said the recruitment consultant.

Like many young women, often in male-dominated professions, Jane has a taste for the high-alcohol drink. "I basically drink it because it doesn't give me as bad a hangover as wine, but you get just as pissed.

"If I'm going out for dinner I drink wine, but if we're going 'out out' - like to the bars or a club - I always drink vodka. It costs more because I don't drink wine as quickly, but I get shocking on wine whereas with vodka I'm not so bad."

For tonight's celebrations, Jane and her friends have made some 40 vodka jellies using one litre of vodka, and a gallon of punch containing two litres - to start.

Jane explained: "Last party my flatmate kept adding more. There were about six bottles in there in the end - but it was a massive vat and there were about 60 people drinking it. It wasn't just me!"

Jane is aware of the health warnings, but is waiting for her body to tell her when to cut down. "You have to have something to make the most of the weekend, don't you?"