Savers should not rely on building society claims that mutual organisations are offering customers a better deal, according to a new survey.

''Contrary to popular belief the top savings rates are not always offered by building societies,'' financial information group Moneyfacts said as the battered ranks of the Building Societies Association assembled in Bournemouth for their annual conference.

''While surveys have shown that mutuals have offered better standard variable mortgage rates, no-one has up to now checked how their performance compares in the savings side,'' Moneyfacts said.

The survey shows that the top five no-notice accounts, at seven tiers ranging from #500 to #50,000, feature only four building societies (one of them, First National, is about to become a bank) and nine banks.

The new banks such as Scottish Widows, Safeway, Standard Life, and Legal & General are prominent, while most of the converted building societies have at least one entry.

On the top five notice accounts, the still-mutuals (excluding Dublin-based First National) take 14 of the 35 places. The banks, including Investec, Royal Bank of Scotland, and the converted Bristol & West, take the rest.

Moneyfacts said it recognised the danger that new banks would offer rates that were ''just a flash in the pan designed to lure people away from their present bank or building society, only to be followed by a lowering of rates when depositors are tied in''.

But it has monitored its own savings tables for the past 12 months to assess how the new accounts have performed. ''The news is encouraging. Since their launch Standard Life and Safeway have appeared every month (in the tables), while Abbey National (Bonus Postal), Alliance & Leicester (Instant Direct), Cheltenham & Gloucester (Instant Transfer), and Scottish Widows (Instant Access) have also featured regularly.

''The mutual flag is being flown by the Coventry building society who have appeared on a regular basis in both the instant access and notice account sections.''

Moneyfacts said: ''Building societies claim that because of their branch structure they cannot always offer good rates, but is this an argument that the members should accept?''

Nationwide, the largest and most vocal of the mutuals, has this year been emphasising on an almost weekly basis how its mutuality delivers keener rates for both borrowers and savers.

This week the newly-elected chairman of the Building Societies Association, John Heaps, told the BSA conference that it was ''impossible'' for banks to show a long-term commitment to the mortgage market.

He added: ''An effectively managed mutual organisation can operate on slimmer margins than a bank and still afford to take a longer term view.''

But the latest survey will be seized on by new entrants such as Standard Life Bank, which is mopping up money at the rate of #100m a month. The bank is understood to be requiring a margin of less than 0.25% on its savings business, but planning to launch mortgage products to re-lend the money on better margins.

Standard Life marketing director Tom King commented this week: ''We estimate that each of our telesales operators is taking in the same amount of cash as 11 building society branches. We expect to take about #1260m over the year, and we have given a commitment that we will be consistently at a good rate and will not penalise existing customers.''

Nationwide does feature in the Moneyfacts tables, appearing twice in the no-notice account section.

The society's Mark Hamilton said more than half of the total number of places in the tables were taken by mutuals (including First National) which was ''a pretty high percentage''.

He added: ''The survey is looking at a narrow section of the market. Other things such as regular savings accounts, Tessas, and children's accounts are not covered, where Nationwide and other building societies perform strongly. The new entrants have brought out products with very attractive rates in some cases, but it is important to look long-term. We offer a range of products and are committed to providing excellent value across the whole range.''

James Evans at Bradford & Bingley, the second largest mutual, observed that the top place in four tiers of the no-notice tables was occupied by Northern Rock, which only last week was forced to abandon its attempt to move many savers compulsorily into lower-rated accounts. He added: ''Alliance & Leicester have a lot of obsolete accounts paying much less than their top rates. We have a policy of having no obsolete accounts whatsoever.'' The society also offers market-beating rates on Tessas and regular savings accounts.

Evans said: ''Safeway are new into the market, just like Tesco and Sainsbury were last year. But Tesco and Sainsbury have now slashed their rates back. New banks which do not yet have massive balances can keep rates higher. The fact is that when it comes to the net interest margin, mutuals retain for themselves an awful lot less than banks.''