The government is to ban the sale of alcohol at very cheap prices in England and Wales, the Home Office has announced.

Ministers hope the move, which will come into force on 6 April, will stop the worst instances of deep discounting, which has resulted in cans of lager being sold more cheaply than water in supermarkets.

An official impact assessment says the ban on sales of alcohol at below cost, defined as duty plus VAT, will mean an ordinary 440ml can of beer or lager cannot be sold below 50p.

The new "floor price" for a bottle of wine will be £2.24; a bottle of vodka or other spirits will cost a minimum of £10.16.

Low-strength beers that have an alcoholic content of 1.2% or less will be exempt from the policy, as will duty-free sales on ships, aircraft and in airports.

Health campaigners accused ministers of buckling to pressure from the drinks industry last July when they rejected a minimum unit price for alcohol and a ban on multi-buy promotions.

The Alcohol Health Alliance, which includes the medical royal colleges, said the impact of the alternative ban on selling at below duty plus VAT would be negligible.

The Home Office's impact assessment published on Tuesday acknowledges the move is only likely to hit 1.3% of all alcohol sales, mainly in supermarkets, but says that this amounts to sales of 220m litres a year.

An explanatory memorandum alongside the parliamentary order introducing the ban says the "government is committed to ensuring the worst cases of cheap alcohol are banned from sale".

Ministers insist below-cost selling is a real issue, with six out of seven major supermarkets found to be selling alcohol at up to 12% below cost in a 2008 Competition Commission study.

They also point to growing evidence of "pre-loading", with two-thirds of young people who were arrested for alcohol-related crime and disorder in one English city admitting they "tanked up" with cheap supermarket booze before going out.

The official impact assessment estimates the move will lead to savings of £5.3m a year in health benefits and £3.6m in crime savings. Annual costs are put at £5.3m including lost duty and VAT revenue and enforcement costs.

The ban will be imposed by introducing a mandatory licensing condition on all those who sell alcohol, including small off-licences. Officials say they do not expect sales from outside England and Wales via the internet to be a significant issue but will keep it under review.

Eric Appleby, chief executive of Alcohol Concern, dismissed the move: "The idea that banning below-cost sales will help tackle our problem with alcohol is laughable, it's confusing and close to impossible to implement. On top of this, reports show it would have an impact on just 1% of alcohol products sold in shops and supermarkets leaving untouched most of those drinks that are so blatantly targeted at young people.

"The government is wasting time when international evidence shows that minimum unit pricing is what we need to save lives and cut crime."

But Home Office minister Norman Baker said the government was determined to tackle the £11bn a year cost of alcohol-fuelled crime: "Banning the sale of alcohol below duty plus VAT will stop the worst examples of very cheap and harmful drink," he said. "It is part of a wide range of action we are taking, including challenging the drinks industry to play a greater role in tackling alcohol abuse."