The insurance giant, whose shares will begin trading tomorrow at £2.30, said it had sent at least three letters to each of the missing policyholders. Their stock will now be held in an Unclaimed Assets Trust until they get in touch or for a maximum of 10 years, after which it can be sold to benefit charities.

The average windfall at the offer price is £1,475 but individual payouts vary depending on policy values and the length of time for which the investments have been held.

The Edinburgh-based insurer will go straight into the FTSE 100 as the UK's fourth-biggest life insurer, behind the Prudential, Aviva and Legal & General, and narrowly ahead of Friends Provident when it floats on the stock market, releasing windfalls for 2.4 million customers.

About 600,000 policyholders have signalled their intention to sell immediately, however this will still leave 75% of the company owned by small investors.

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