Lord Neill's Committee on Standards in Public Life is to recommend a code of practice for government advisers, the BBC has learned.

It follows opposition concerns over their growing numbers and influence.

The committee has been reviewing the conduct of ministers, MPs and civil servants and it will publish its report on Wednesday.

There are currently 74 "special advisers" such as Prime Minister Tony Blair's press secretary Alastair Campbell - twice the number under the last Conservative government.

With many new ministerial posts being created in Scotland, Wales and Northern Ireland since devolution, Conservatives and Liberal Democrats have expressed concern that the numbers may soon exceed 100.

Advisors under scrutiny

The opposition parties say that, without tighter controls, Labour could build up a campaign team for the next election at the tax payers' expense.

Lord Neill's committee is to recommend taking a "hard look" at the "expanding political power base" of advisers.

Previous recommendations by the committee include coming out in favour of tight restrictions on anonymous donations to political party funding.

In a report which came out in February 1998, Lord Neill said individuals giving more than £1,600 should be identified. He also called for an end to foreign donations.

Lord Neill began his inquiry late in 1997 when the Labour Government was embroiled in a row about a donation from the controller of Formula One motor racing , Bernie Ecclestone.