Former spy chief Scarlett will step out of the shadows next week

John Scarlett, one of the least-known but most influential figures in the establishment, will be thrust into the spotlight when the Hutton Inquiry reconvenes after the Bank Holiday.

Until last year, governments had refused even to confirm the identity of the chairman of the Joint Intelligence Committee (JIC). The practice changed when the former MI6 officer was appointed to the body that advises the Government on intelligence materialn.

That was as far as the new spirit of openness went and Mr Scarlett retreated to the shadows. But on Tuesday, as the author of the Government's September dossier that made the case for war, Mr Scarlett will undergo a forensic public cross-examination on its compilation. Alastair Campbell, Tony Blair's director of communications, last week repeated the Government's insistence it brought no pressure on the JIC to toughen the dossier between drafts. He told the inquiry he had "no input, no output or influence" on the document, only advising on its presentation.

Mr Scarlett will be challenged on the truth of that and how it squares with the stream of e-mails from Downing Street discussing the tone and style of the planned dossier. Questioning will focus on a memo from Mr Campbell to Mr Scarlett, whom he has described as a friend, which pointed out that the language about chemical and biological weapons was weaker in one part of a draft version of the dossier than another. A day later Mr Scarlett replied that "the language you queried ... has tightened".

The JIC chairman will also be put on the spot over his demand that David Kelly be hauled back for a "proper, security-style interview" after his initial grilling over his contacts with BBC reporter Andrew Gilligan. The inquiry will want to know whether this interview was as menacing as it sounded, the inference being that it could have affected Dr Kelly's state of mind shortly before his apparent suicide.

Mr Scarlett will be followed by Sir David Omand, the Prime Minister's chief security co-ordinator, who was closely involved in the Whitehall response to Dr Kelly's admission he met Mr Gilligan.

But first into the witness-box will be Labour MP Andrew MacKinlay, who put some of the most aggressive questioning to Dr Kelly at his fateful Foreign Affairs Select Committee appearance.