But a report compiled by retail analysts Verdict suggests that this an unfair judgement.

The four big supermarket chains, Tesco, Sainsbury's, Asda and Safeway account for almost half the UK's grocery sector, which this year grew to £97bn.

Tesco is one of the four big supermarkets under investigation by the Office of Fair Trading

But disquiet over the profitability of these companies and over the prices being charged in the UK, compared with prices in mainland Europe, led to an investigation by the Office of Fair Trading. Its conclusions are expected this month.

At question is whether there is enough competition between supermarkets to ensure the customer is getting a good deal and whether the low prices that supermarkets can demand from suppliers are being passed on to consumers.

Shares in the leading supermarkets have risen steadily since the mid-90s and have grown particularly strongly in the last two years.

It has led to accusations that shareholders are benefitting at consumers' expense.

But according to retail analysts, Verdict, the UK grocery supermarket is too competitive for companies to be able to sustain unreasonably high prices.

A spokesman said: "We do not believe Britain's grocers are overcharging."

Verdict claims UK supermarkets are not more profitable than those in Europe.

It is just that UK companies maximise profits to reward investors while the privately-owned continental supermarkets minimise profits to avoid paying tax.

The report also claims that the high quality of the food and surroundings in UK supermarkets means that shoppers will pay more to shop there.

It claims that the operating margins of the big four supermaket chains have fallen over the past five years and it says the current economic slowdown will force them to focus on price.

Price war danger

However Verdict warns that any price war could see some companies forced out of the sector altogether.

A Verdict spokesman added: "With all the players growing at similar rates, the temptation to outperform through a dramatic move on pricing is growing