Dr Tony Wright, chairman of the Public Administration Committee, told the BBC it could be possible to make Tony Blair answer to Parliament over the growing number of special advisors.

There has been criticism that the network of advisers amounts to an unofficial prime minister's department in Downing Street.

When John Major left Downing Street he employed eight special advisors accountable solely to him.

Now the prime minister has 21 special advisors, such as his chief press spokesman Alastair Campbell.

Tony Blair: Could answer to committee

Dr Wright said: "Would it be proper for a prime minister, albeit unprecedented, to come and give evidence to a select committee about some of these developments? I think it would.

"I think it would be a continuing thing if we do see the development of something like a prime minister's department, even if it's not called that, then I think Parliament, very properly, would want to consider how it responds to that.

"One of the ways it would do it would be seeking to bring that department under the normal accountability mechanisms."

Conservative MP Andrew Tyrie has said he will submit a paper to the Committee on Standards in Public Life on the issue.

He said: "I think the time has come when we need a cap on the number of advisors and a cap on the amount spent."