The letter highlights the current partial amnesty being offered by HMRC to those that have unpaid taxes owing.
This ends on June 22 after which time they could face large fines or criminal prosecution. A copy of the letter, which HMRC is sending out tomorrow, can be found here.
Only around 8,000 people have taken advantage of the amnesty. Under the terms of this arrangement people have to pay all tax and interest owing along with a 10 per cent fine.
After the June 22 deadline a HMRC spokesman says it will begin investigations which will potentially lead to 100 per cent fines and possible criminal prosecution.
The letter says: “After June 22, HMRC will begin to investigate individuals with offshore bank accounts who appear to have tax to pay but have not notified us that they want to make a disclosure, and the penalties will be much higher than under the disclosure arrangements.”