While a few thousand expatriates are threatening to sue the Halifax for excluding them from last summer’s windfall, the new bank is still trying to find nearly 200,000 members in Britain who failed to claim free shares.

As the unclaimed parcels of stock are worth an average £2,600 at the current market price, the total value of these forgotten windfalls is £520m.

Unlike the UNited HAlifax Victims - or UNHAVS as the disgruntled expats call themselves - who may end up in court fighting their eligibility case, members resident in the UK need only write to the Halifax or visit a branch to stake their claim.

A Halifax spokesman said: "People who have not claimed their shares may have moved house but not given us their change of address." Halifax is sending letters to all non-claimants reminding them of their windfall shares.

The average allocation was 330 shares, worth about £2,400 at the first-day closing price of 732½p. However, the shares, down from a high of 977p, are currently trading at about 803p.

UNHAVS were excluded by the Halifax if, say, they live in a non-permitted territory such as Canada or New Zealand. The spokesman said: "Certain countries were excluded because of local laws or tax regimes. Other members do not have a registered address in Britain."