LONDON (Reuters) — The taxman is writing to 200,000 people urging them to come clean over any unpaid taxes on offshore accounts.HM Revenue & Customs (HMRC) said yesterday it would be sending the letter from today to around half of the 400,000 people it believes might have failed to disclose tax liabilities on offshore accounts.

It comes little over a week before the deadline of a tax "amnesty", allowing people with offshore accounts and overseas property to disclose income and gains not previously put on their tax returns — without being hit by hefty penalties.

Under the "offshore disclosure facility", investors have until June 22 to notify HMRC of their intention to declare unpaid tax dating as far back as 198[7/8]8.

But, so far, only 8,180 people have come forward.

Steve Besford, head of tax investigations at independent tax adviser Chiltern and a member of the liaison group that has been working with HMRC on the amnesty, said the move smacked of "desperation".

He told Reuters: "There's never been any indication that this was part of the plan; it's really a bolt out of the blue.

"Publicly, the Revenue is saying the whole initiative has been a success, primarily because it's a different way of approaching compliance, so any take-up means it's a success.

"But secretly, I think it will be disappointed with the number of notifications it's had: 8,000 out of 400,000 is a pretty poor return."

However, a spokesman for HMRC denied it was a panic measure.

"This is part of a customer service exercise: we always planned to do it to give people the opportunity to come forward," the spokesman said.

Those who register for the amnesty by a week on Friday and pay outstanding tax and interest by November 26 could be spared a full investigation, and penalties — which could otherwise be up to 100 percent — will be capped at 10 percent.

Besford believes the letter — from David Hinstridge, HMRC's offshore disclosure arrangements project manager — will spark a last-minute rush, akin to what happened under a similar amnesty in Ireland, which raised some $580 million pounds for its Treasury. Then, some 80 percent of notifications were made in the two weeks leading up to the deadline.

"A lot of people have been dithering about this and many believe the Revenue hasn't got anything on them and, if they do, they think it will be pre-occupied with bigger and better things," said Besford.

"But, I think this letter will drive the message home that the Revenue is interested in anyone with unpaid tax."

The government won a series of legal battles to obtain details of offshore account holders last year — the most high-profile case involving Barclays.

It and another four banks — HSBC, HBOS, Royal Bank of Scotland and Lloyds TSB, according to media reports — were forced to hand over customers' details.

But despite the lower penalties on offer, HMRC has reserved the right to prosecute, stating that it many open formal enquiries, particularly in larger cases of tax avoidance.

Reg Day, KPMG's director of tax investigations, warned that those who fail to declare unpaid tax from offshore accounts are likely to face vigorous investigation.

"It's difficult to fathom why so few people have so far come forward to register," he said.

"It may be that there is a 'herd' mentality operating here and people are under the impression that there is safety in numbers — if they hide in the crowd HMRC won't be able to get them."