Britain's supermarket giants are expected to consolidate their position as the nation's biggest retailers during the next 10 years, a report predicted today.

But the flagging fortunes of traditional traders such as Marks & Spencer could plummet further.

Analysts at Retail Intelligence said a decade on decade forecast showed the major supermarkets, which currently occupy the first four places with combined sales of more than £46bn in 2000, are also likely to lengthen their lead as consumers' favourite places to shop.

However, they may have to continue diversifying with the internet expected to play an even bigger role by 2010.

That medium, tied to a continuing high street presence, was likely to be a winner during the coming years, said Retail Intelligence.

The predictions were not so good for stores like Marks & Spencer with the report warning the firm could slide even further down the pecking order.

A spokesman said the chain's problem was partly caused by its attempt to be "all things to all men", the same ploy which it said eventually forced rival chain C&A out of business in Britain earlier this year.

"Recovery at M&S, if it is to happen at all, can only be very slow because the business has undermined the trust of its customer base," he said.

"There is still a place in the market for M&S's strategy producing well made clothes which are moderately fashionable but produced at highly competitive prices.

"But such a strategy can only work if the company maintains its quality standards. In the quest for ever higher operating margins in the 1990s, those quality standards slipped."

M&S spokesman Louis Hill said Retail Intelligence's figures showed the chain was still the biggest UK clothing retailer, while insisting that it had the right strategy in place to reverse its fortunes after it recently posted its lowest profits for 14 years.