Lord Hutton will today rule on whether the Ministry of Defence failed to carry out its duty of care for Dr David Kelly.

As the employer of the former government scientist, the Whitehall department is perhaps most vulnerably placed if the law lord directs any substantial criticism at the government.

It was to MoD managers that Dr Kelly suggested on June 30 that he might be the source of Andrew Gilligan's controversial reports for the BBC.

And it was MoD press officers who confirmed his name as the suspected source to journalists from three national newspapers.

The position of defence secretary Geoff Hoon is vulnerable as he will be required to accept political responsibility for the actions of his officials.

However, in an apparent rearguard action, his top civil servant has sought to lay the blame for the naming of Dr Kelly at the door of Number 10.

"A policy decision on the handling of this matter had not been taken until the prime minister's meeting," said Sir Kevin Tebbit.

Another key decision for Lord Hutton relates to whether the MoD adequately supported Dr Kelly after his name became public.

Richard Hatfield, the department's personnel director, described the support as "outstanding".

But that is bitterly disputed by the Kelly family, which has described how the scientist was forced to flee his family home with 10 minutes' notice that his name was about to become public.

If Lord Hutton rules that the MoD failed to honour its obligations to the late scientist, opposition parties will call immediately for Hoon's resignation.