Investors will be able to withdraw their money within seven days of committing themselves without penalty.
Cooling-off periods, normally of 14 days, are mandatory on many investments regulated under the Financial Services Act.
But the new breed of bonds offering a return linked to stock market performance are classed as building society accounts with an interest rate usually linked to the FT-SE 100 index.
The Building Societies Commission is issuing a prudential note to societies advising them to offer seven- day cooling-off periods on the bonds. Existing bondholders will not benefit, but the cooling-off period will apply to all bonds sold from next week.
The commission is concerned that investors may not fully understand the differences between the bonds and traditional building society deposits. Societies are also being warned to ensure that they do not exaggerate returns from the bonds.
Millions of pounds have already been invested in the bonds, which normally offer a gain linked to growth in the stock market over a set period, typically five years.
There are guarantees that investors will get back what they originally invested. Societies are using futures and options contracts to secure the stock market-linked gains.
Similar products have been marketed widely by insurance companies, and the life insurance regulator, Lautro, this week warned its members about exaggerating returns.
The regulator also said some companies may need to write to existing investors if there is a possibility that they bought the bonds 'under a misconception'.
It is understood that the Building Societies Commission will instruct its members to follow Lautro's guidance when marketing these bonds in future.
Lautro is worried that not all advertisements for guaranteed equity bonds make it clear that investors' returns will be reduced by charges and tax. It is also worried about whether early-surrender penalties are being made clear enough.
Lautro's enforcement bulletin says: 'A number of members have issued advertisements showing guaranteed returns against the FT-SE 100 Index expressed in 'gross' terms. This is potentially misleading where the underlying funds of the member concerned are taxable and the returns quoted are therefore unavailable to the investor in any circumstances.'
Laurentian Life is one company that did quote gross returns on its Capital Protected Bond, marketed at the end of last year. Yesterday Tony Worthington, head of marketing services, said the company was now considering whether it should write to investors.
Between pounds 2m and pounds 3m had been invested in the bond, which offered 115 per cent of gains in the FT-SE 100 over five years.
While the company had quoted a gross return, he believed it had made clear to investors that this was subject to tax.
Northern Rock Building Society is promoting gross returns on its Guaranteed Equity Bond, available until next Thursday. Marketing literature tells investors that if the FT-SE 100 goes up over the five years of the bond's life, the value of the investment rises by the same percentage. 'If share prices rise only slightly or even fall, you're still guaranteed a return of 15 per cent gross as well as your investment back in full.'
The brochure goes on to explain in smaller print that the returns will be paid net of basic rate tax, which may be reclaimed by non-taxpayers.
Adam Applegarth, assistant general manager of Northern Rock, said he did not see any need to write to investors who had already put money into the bond. But if the society was to offer another one, it might give more prominence to the post-tax returns in its promotional literature.
The FT-SE 100 has risen by about 1 per cent since the beginning of the year, when these bonds began to be heavily sold.
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