The government's proposed minimum price for alcohol has been set so low it would have stopped only one cut-price drink deal out of thousands in the last three months, a Guardian investigation has found.

The UK's four leading supermarket chains had 3,667 cut-price alcohol deals in the last three months, according to data provided by promotions consultancy Assosia, and none of the products would have increased in price under the new rules.

The changes would not have affected promotions such as a Tesco special deal offering 24 cans of Fosters for £10, or three 15-packs of Strongbow cider – totalling 89 units of alcohol – for £20.

The coalition government agreement drawn up last May agreed to "ban the selling of alcohol below cost price".

The proposals, introduced last month by the Tory Home Office minister James Brokenshire, would bar the sale of alcohol at below the cost of duty and VAT. This sets a floor price of 38p for a can of lager, £2.03 for a bottle of wine, or £8.00 for a 700ml bottle of spirits.

"Banning the sale of alcohol below the rate of duty plus VAT is the best starting point for tackling the availability of cheap alcohol and will send a clear signal to retailers and the public that government take this issue seriously," Brokenshire said when he introduced the bill in parliament.

"They will effectively set a minimum level below which alcoholic products cannot be sold and will stop the worst instances of deep discounting, which result in alcohol being sold both cheaply and harmfully."

The Guardian's findings provide the first solid evidence supporting concerns raised by health groups in the wake of the announcement that the pricing level was set too low. Shadow public health minister Diane Abbott said the findings showed the government had given in to industry on alcohol pricing.

"The government's actions on minimum alcohol prices have been completely phoney," she said. "They must have realised that the minimum price they were suggesting would have hardly any effect. Obviously, the drinks industry must have been very glad that the government appears to be taking action on pricing, but in practice is doing nothing. This just shows how when it comes to public health, Andrew Lansley puts the interest of big business first."

Health professionals have called for stronger proposals on alcohol pricing for several years. In 2009 Liam Donaldson, then the country's chief medical officer, proposed a 50p a unit minimum price on alcohol, which researchers at Sheffield University estimate could reduce drink-related deaths by 3,000 a year.

This would have increased the price of 349 supermarket promotions in the last three months, but over 90% of supermarket drink deals would be unaffected by even this higher unit price.

The Home Office defended the proposals as a "starting point" for the government's plans to deal with below-cost selling.

"The government believes that a minimum price of duty plus VAT is the best starting point for tackling the availability of below-cost alcohol, as we committed to in the coalition agreement," said a spokesman.

"In its investigation into the groceries market in 2008, the Competition Commission found that alcohol is one of the main product groups which are sold below cost by the leading retailers.

"The impact of alcohol prices on public health and crime and disorder is a complex one and we will continue to consider further how to tackle this issue."

Supermarkets ran 15,746 alcohol deals in 2010, the Assosia data reveals, of which almost 5,000 required customers to buy multiple products to receive a discount. The Royal College of Physicians and Alcohol Concern have expressed opposition to multi-buy deals, and have called for a ban on advertising such offers.

Assosia collects its weekly data by sending researchers into several stores from each of the UK's largest supermarkets – Tesco, Asda, Sainsbury's and Morrisons – to collect information on all high profile promotions in store. As supermarkets refresh their promotions weekly, each week of a long-running promotion is counted as a sepearate promotion.

• This article was amended on 24 February 2011. The orginal said that Asda sold Grant's whisky for £11 in its stores just before Christmas and that Sainsbury sold a 24-pack of Boddingtons for £10. This has been deleted. Asda has asked us to make clear that the lowest price for Grant's whisky in that period was £15.97, and that it has a policy not to sell alcohol at below the cost of duty plus VAT, the government's proposed minimum price for alcohol. The research company Assosia, which supplied all the data, has also confirmed that Sainsbury's did not sell Boddingtons at that price.

Cheapest supermarket drinks deals

The government has rejected unit pricing of alcohol in favour of a duty-plus-VAT minimum. Health professionals say a 50p-per-unit floor price could save 3,000 lives a year.

1. Strongbow 24x440ml

Cheapest selling price: £10.00

Store: Tesco

Number of units: 47.5

Price per unit: 21p

2. Fosters 24x440ml

Cheapest selling price: £10.00

Store: Tesco

Number of units: 42.2

Price per unit: 24p

3. Stella Artois 12x440ml

Cheapest selling price: £6.67

Store: Tesco

Number of units: 26.4

Price per unit: 25p

4. Gaymers 12x440ml

Cheapest selling price: £6.00

Store: Morrisons

Number of units: 23.8

Price per unit: 25p

5. First Cape Merlot 3l

Cheapest selling price: £12.00

Store: Asda

Number of units: 40.5

Price per unit: 30p

6. Bombay Sapphire 1l

Cheapest selling price: £12.50

Store: Tesco

Number of units: 40

Price per unit: 31p

7. Peroni 6x500ml

Cheapest selling price: £5.00

Store: Asda

Number of units: 15.6

Price per unit: 32p

8. 35 South Cabernet Sauvignon 75cl

Cheapest selling price: £3.33

Store: Asda

Number of units: 9.8

Price per unit: 34p

9. Smirnoff Ice 12x275ml

Cheapest selling price: £6.49

Store: Sainsbury's

Number of units: 16.5

Price per unit: 39p

Source: Assosia