Alistair Darling announced yesterday that it will cost the Treasury £800 million to fund the compensation of 240,000 British depositors with Icesave, the collapsed Icelandic bank.

The cost of the rescue package emerged as the Financial Services Compensation Scheme (FSCS) came under fire for contacting Icesave customers by e-mail, rather than by letter, with details on how to reclaim their money.

Many savers have complained that they have not received the e-mail, while security experts say that fraudsters may be contacting Icesave customers with phishing e-mails, inviting them to input financial details into a fake Icesave website.

Mr Darling said that the Bank of England would lend the FSCS £800 million, financed by the Treasury, to meet his promise that no British depositor in Icesave would lose money.

A spokesman for the Treasury said it hoped to recover the £800 million through continuing negotiations with the Icelandic Government. The British Government, meanwhile, has threatened to sue the Icelandic authorities if they do not honour their obligations towards British savers.

Icesave depositors have been unable to access their funds since the bank's parent, Landsbanki, collapsed on October 7 and became nationalised. The FSCS usually guarantees deposits of up to £50,000 but has promised to refund all deposits.

An initial e-mail tells savers how the process works while a second e-mail will invite depositors to log on to their existing Icesave accounts to receive their compensation.

A spokesman for the FSCS said that e-mail was the quickest and most efficient way of contacting customers. Some savers have already complained that their spam facility has blocked the e-mail because it looks like a phishing attempt. Phishing is where fraudsters try to steal financial information using bogus e-mails.

Internet security experts say that the FSCS's decision to contact savers by e-mail has left depositors vulnerable to this type of scam.

David Holman, of First Cyber Security, an online security company, said: “Putting savers who are desperate to get their savings back at this level of additional risk is inexcusable. Most banks actively discourage the use of e-mails to communicate with customers, as fraudulent e-mails giving fake website links are prevalent.”

A spokesman for the FSCS said: “We have asked Icesave customers to note that no one from FSCS will contact them by phone or e-mail to check their bank account details. There will be no links in any of the e-mails sent from FSCS.

“We will be using the existing Icesave website to pay compensation and the logon process to claim is the same as it would be when normally accessing their Icesave accounts.”