A cap should be imposed on the number of special advisers employed by the government, an influential committee of MPs has recommended.

In its report, the Labour-dominated public administration select committee called for the measure to be included in the long-awaited civil service bill.

Such a figure would be decided at the beginning of each parliament, approved by resolutions from both the House of Commons and the House of Lords.

The committee is currently in the process of drawing up its own bill, which will also call into question the right of the prime minister to appoint up to three personal assistants with management power over civil servants in Downing Street.

Tony Blair currently has two - director of communications Alastair Campbell and chief of staff Jonathan Powell.

The number of special advisers and their role came under intense scrutiny after Jo Moore, a former spin doctor to former transport secretary Stephen Byers, suggested that September 11 was a "good day to bury bad news."

"There is a pressing need for parliament to play a more active role in helping to maintain ethical standards in the public service," said committee chairman Tony Wright.

"A bill would make sure that long-standing public service principles like impartiality and integrity were underpinned by proper parliamentary debate and discussion, and that proposed changes had a full airing."