Her Majesty's Revenue & Customs (HMRC) is trying once more to claw back money from people with offshore bank accounts through the offer of a partial amnesty.

The move follows an attempt to offer offshore account holders an amnesty in June 2007 which has produced meagre pickings for Revenue & Customs .

From early next year, HMRC will announce a second partial amnesty designed to persuade holders of offshore accounts to reveal the tax that they owe in exchange for a reduced fine.

HMRC will demand that 150 UK banks and other financial institutions with offshore branches supply full details of customers' offshore accounts.

"The cash in the offshore bank accounts may only be the tip of a very large iceberg," said Ronnie Ludwig, partner in the wealth management practice of accountant Saffery Champness in Edinburgh.

"The talk is of an amnesty on the tax due on the interest earned on the offshore accounts, but I think the real reason many of the offshore account holders have not come clean thus far is that the principal capital in these accounts may itself be taxable, not just the interest.

"The capital could be derived from covert offshore businesses, internet trading such as on eBay, or from foreign capital gains."

Dave Harnett, director-general of HMRC, last week said: "We have had a meeting with 150 (banks) and will be serving information notices to bring more info into our net."

The banks are unlikely to be able to resist HMRC's request to divulge the identities of offshore account holders. Armed with this information, HMRC will offer all the account holders a "disclosure arrangement" - or a partial amnesty.

Harnett suggested the terms will be similar to those in June's amnesty. At that stage, 100,000 people with accounts held in offshore branches of seven of the UK's largest high street banks, often in tax havens such as Guernsey and Jersey, had their fines capped at 10% - so long as they owned up and paid their back taxes with interest.

About 64,000 taxpayers had come forward by HMRC's June 22 deadline. These people now have been given until November 26 to pay what they owe, plus a fine. Should they fail to do so, HMRC says its initial offer will be withdrawn.

So far 20,000 taxpayers have taken up the offer, reaping a £120m dividend HMRC. However, this fell short of the estimated £2bn of unpaid tax held in offshore accounts and was less productive than amnesties offered by other countries such as Ireland. One reason the uptake has been low so far is that HMRC still reserves the right to prosecute, even those who meet the deadlines.

Ludwig added: "Doing nothing is not an option. At the end of the day, we are all mortal and the account holders will die.

"If they have not declared the offshore accounts and income before, the problem will be left to their spouses and children, who will not only inherit the accounts, but will also inherit the tax problem. The liability does not die with the account holder and beneficiaries will be faced with an HMRC investigation ..."