Standard Life members have been promised a shares windfall after the society fired the starting gun on a plan to list on the stock market.

The long-awaited move, which will end the assurer's 80 years as a mutual, will see around 2.4 million eligible policyholders receive shares in place of their membership --estimated by analysts to be worth up to £1,000.

Edinburgh-based Standard set out the timetable for the process yesterday , with the proposals due before members in May or June.

The mutual requires the support of 75 per cent of those who vote if the demutualisation and flotation is to go ahead.

Standard, which is expected to be worth between £4 billion and £6 billion when it lists next summer, signalled its intention to float in March 2004.

At that point new Standard members were asked to sign a waiver ruling them out of any windfall should the company pursue a demutualisation.

The board confirmed its backing for the listing move, banishing fears that ongoing regulatory talks with the Financial Services Authority may cause the process to be put back.

Standard will write to all eligible members before the end of October to ask them to confirm their policy and contact details.

Standard Life added that anyone who buys a policy on or after October 18 would not be eligible for membership rights.

Chairman Sir Brian Stewart said: "The board continues to believe that demutualisation and flotation is the best way forward and in the best interests of members, customers and the company.

"We expect to put proposals to members ahead of a special general meeting next May or June."

Standard said demutualisation was necessary as there were increasing risks to its with-profits policyholders if the company remained as a mutual.

In a mutual business, with-profits investors take on the business risks and rewards of the group. But with the risks being borne by progressively fewer people, Standard said the benefit of a plc meant the responsibility lay more with shareholders and reduced the pressure on policyholders.

A flotation should also give Standard access to external equity which would not be available to it as a mutual.

Standard reversed its longstanding opposition to demutualisation after discussions with the FSA over its solvency position.

Since then it has worked to reposition its business as it prepares for a stock market listing. However, analysts said the valuation will be swayed by outside factors such as the value of the stock market and life insurance stocks, plus investors' views on the strength of the company's balance sheet.