High profile tax evaders will be taken to court "within weeks" says HM Revenue and Customs (HMRC).
About 60,000 people have asked to take advantage of its recent offer to pay unpaid taxes, but with a penalty of just 10%, on cash in offshore accounts.
But an HMRC spokesman said that a further 40,000 people suspected of being significant tax evaders would now be pursued vigorously.
"The consequences start right now," said the spokesman.
Those who have come forward under the HMRC "offer" to pay their back taxes, plus interest and the 10% penalty, have until 26 November to do so.
Examples so far have been a city broker with £300,000 of his city bonuses stashed offshore, a company director with a million pounds hidden in an offshore bank account, and a landlady who had hidden £30,000 in rent.
The HMRC will want to know if income tax or capital gains tax was paid on the original sum before it was put away, as well as whether or not tax has been paid while the money has been accruing interest.
"Some will have to pay gargantuan sums of tax," said the HMRC spokesman.
The taxman will now turn his full attention to those he thinks have not taken advantage of the opportunity to confess.
Its Special Civil Investigations Department (SCI) will cherry pick a few high profile cases for swift criminal prosecution.
"We will get those in the magistrates court quite quickly," said the spokesman.
Local tax offices will sift through the rest.
However the HMRC denied it would choose its victims on the basis of their public profile.
"We are looking for high risk tax evasion based on their criminal behaviour, not their public celebrity," the spokesman stressed.
It is thought that as much as £1.5bn in unpaid tax may now be garnered by the HMRC, now that it has full access to the names and addresses of UK citizens with bank accounts abroad.