Geoff Lister, chief executive at Bradford & Bingley Building Society, said yesterday: "Deciding on a personal pension is an extremely important step.
"It is not like walking into a shop and choosing a set of underwear or fresh fruit. Making the wrong choice can have very dangerous consequences in retirement. That is why it is always important to obtain unbiased independent advice first."
Mr Lister's comments followed an announcement by M&S that it is to move into the life insurance and pensions field next month.
From next month, the company plans to offer a range of financial products, including a pension that aims to protect investors from the worst effect of future stock market crashes.
The M&S pension, managed by Barclays de Zoete Wedd, will track the FT- SE 100 share index. The fund will benefit from any gains in the Footsie, except for dividend income that would normally accrue to the shares concerned.
Instead, this will be used to buy options, to help protect against market falls.
Marks & Spencer's launch is an ambitious plan to link its reputation for quality and trustworthiness to the sale of life insurance and pensions.
Robert Colvill, managing director of Marks & Spencer Financial Services, said: "We cannot offer an absolute guarantee, but we can protect against the risk of a more serious market fall happening, such as the October 1987 crash."
In addition to pensions, the company will offer a range of financial products by mail order, including critical illness and family protection plans.
Potential buyers will be able to pick up product brochures from any of the company's stores and call a freephone number linking them to an admin centre in Chester. Trained staff will answer any technical query over the phone but will not actually push these products to clients. They will be sold on an execution-only basis.
If clients buy an M&S pension or another product, the company says it will give them a 30-day money-back guarantee period, more than double the time normally offered by other firms.
M&S is clearly aiming to capitalise on its name and reputation - and relative aversion to risk of the millions of customers who already shop in its stores.
Keith Oates, chairman of Marks & Spencer's financial services arm, said: "Our aim in designing these products has been to provide life assurance and pensions plans which reflect the M&S traditions of quality, value and service. We will be promoting them with the simplicity and clarity we know our customers are looking for."
The pension scheme's charges include a bid-offer spread of 5 per cent, a £1.20 monthly policy fee and a 0.75 per cent annual management fee.
The link between a strong brand name and the offer of new financial products is not new to M&S. It has 3.4 million charge accounts, while 350,000 customers have borrowed almost £900m in personal loans.
For further information call 0800 363422.