Offshore tax evaders are set to be offered a second chance to come clean about their undeclared liabilities under a new offshore disclosure scheme, Accountancy Age can reveal.

The head of tax policy in the UK, HMRC director general Dave Hartnett, revealed the move in a televised interview with Accountancy Age today, and also said that 30,000 people were under investigation following the first of the schemes.

A second 'amnesty', as it was dubbed, will raise questions as to whether such once-in-a-lifetime opportunities are actually that, and may undermine future efforts to persuade tax evaders to come forward.'

We will try and do something similar, on the principle that a repentant sinner coming forward is what we want. We want to offer something similar to those who haven't received letters from their banks. We haven't quite worked out how to do it yet,' Hartnett said.

The tax body is looking to obtain offshore account details for 175 banks and other financial institutions in a bid to widen the net it cast with the UK's top five banks.

Hartnett's reference to the letters sent out by the big banks indicates the new facility will be structured around only those who may have been unaware of the original scheme.

Tax advisers said that the amnesty plan might mean some individuals received unnecessarily harsh treatment, and that the new system would have to be harsher than the first.

'HMRC cannot now offer softer treatment to taxpayers who may have ignored the first [amnesty] solely because they thought they might not get caught,' said Baker Tilly head of tax George Bull.

'It would not be acceptable if the second facility was softer than the first, and it would be invidious if those cases that came to light between the two were treated the hardest.'

The first scheme involved paying full tax, interest and a 10% penalty, though there was no formal cap or indemnity against prosecution. Taxpayers who made a disclosure during the first amnesty have a week left to pay up.

Hartnett said the taxman had recouped £120m so far, with payments expected to hit 'maybe £500m - perhaps a bit more or less'.

As many as 30,000 people are now under investigation on the basis that HMRC thinks they should have made a disclosure, with 1,000 of them thought to involve large sums, Hartnett said.