Life assurer Friends Provident unveiled plans today to convert into a publicly owned firm and said it expected to float on the London Stock Exchange in July.
The 170-year-old company estimated it would have a market value between £3.7 and £4.2 billion putting it in the league of London's largest companies which make up the blue chip FTSE 100 index.
Most members will be in line for a windfall of between £450 and £540 in shares, but some could get substantially more, depending on the type of policy and how long they have held it.
Friends Provident will raise 1.4 billion pounds of net new capital through an offer to institutional investors and members.
It said its advisers, investment bank Merrill Lynch, had indicated a share price of between £2.25 and £2.70, based on the mutual's data a week ago.