Campbell likely to snub adviser inquiry

The Prime Minister's two most senior aides are unlikely to give evidence to a high-level investigation into the role of special advisers.

Alastair Campbell, Tony Blair's strategy and communications guru, and Jonathan Powell, his chief of staff, are expected to refuse an invitation from the Committee on Standards in Public Life, which began an inquiry yesterday.

Downing Street hinted that it would not depart from a "convention" that Government officials do not appear before committees. "We have received an invitation for both of them. It is still under discussion," a spokesman said.

The inquiry, which is led by Sir Nigel Wicks, will look at whether there are too many special advisers in government and whether they have put pressure on civil servants to abandon the convention of political neutrality.

Martin Sixsmith, who was press chief to the former transport secretary, Stephen Byers, until February, has also been invited to attend the hearings. But the Government has warned him not to give evidence that would risk breaching the terms of his severance deal.

Mr Sixsmith is understood to have written to Sir Nigel saying that he would be delighted to attend but is bound by constraints and is therefore reluctant. The committee has told Mr Sixsmith that he can give evidence on any day of the inquiry, which finishes next month.