The bill will follow a report to be issued today by the Securities and Investments Board, the City watchdog, into bad advice over the shifting of occupational pension schemes into private ones.
Last night, sources said that the SIB paper, which is more than 100 pages long, could prompt 300,000 more people who were wrongly advised to claim compensation.
The regulator's initial estimate of claimants, based on a review set up last year, was aimed at so-called 'transfer' cases, in which people who had already left jobs were advised to move their funds out of their previous employers' schemes and into private ones. The review estimated that the number likely to be affected in this way could be up to 40,000, with the total cost of reimbursing them running to between pounds 200m and pounds 300m.
However, research for the SIB by Bacon & Woodrow, independent actuaries, has uncovered a far larger number of opt-outs - people still working for an employer who were persuaded to leave that scheme and set up a personal pension instead.
The assumption will be that advice to opt out was wrong unless records prove otherwise.
Sources said the new research would show that 300,000 of company clients were treated in this way and that reimbursing them would cost up to pounds 8,000 per head.
The SIB's document suggests that a special pensions unit be set up for clients of independent financial advisers and other sales staff whose firms have gone bust. The claims of these 'orphans' will be considered by the unit.