The monthly cost of administering and the number of calls made to HMRC's tax evasion hotline were the subject of a written question in Parliament.
Secretary to the Treasury Jane Kennedy said that there was no separate monthly record of the cost of administering the hotline, but she gave details of the number of calls made.
The most calls in a month was 29,387 in March 2006, with 11,244 and 11,148 made in February and April 2006 respectively.
More recently, in January to May 2007, the number has ranged from 6,634 to 9,710.