One of the questions is "What is perverting the course of justice?".
Perverting the course of justice is important since it undermines the integrity of the justice system (see, for example, Perjury and Perverting the Course of Justice Considered).
What is perverting the course of justice?
Perverting the course of justice is a common law offence in English Law. It being a common law offence creates difficulties in producing an entirely unambiguous definition of the offence.
A useful, but informal, definition is found here The Elements of the Offence:
The Elements of the Offence.
The offence is committed where a person or persons:
(a) acts or embarks upon a course of conduct,
(b) which has a tendency to, and
(c) is intended to pervert,
(d) the course of public justice: R. v. Vreones
The same source states,
A positive act is required. Inaction, for example, failing to respond to a summons, is insufficient to constitute the offence.
Failing to tell the Hutton Inquiry something might not be an offence since, some might argue, there is no "positive act".
However, being asked a question at the Hutton Inquiry to which an untruthful answer or incomplete answer is given might constitute the offence, it seems to me. Assuming, of course, that a court considers that the other necessary elements of the offence are present.
The Crown Prosecution Service web site has an interesting article on the Charging Standard with respect to perverting the Course of Justice, Public Justice Offences incorporating the Charging Standard.
Who can commit the offence?
It is clear that police officers can commmit the offence, including police officers of considerable seniority. For example in Charging decision regarding Metropolitan Police officer (Jamshid) Ali Dizaei we see that a police officer of considerable seniority can be charged with the offence.
What are the available punishments?
Perverting the course of justice is a serious crime. According to the sentencing guidelines on the Crown Prosecution web site, Perverting the Course of Justice, sentences of up to four years may be imposed for "concealing evidence". For example, Jeffrey Archer received a sentence of four years in relation to concealing the existence of a diary.
According to Charging decision regarding Metropolitan Police officer (Jamshid) Ali Dizaei the maximum punishment for perverting the course of justice is life imprisonment.
How might this apply to David Kelly's death?
Concealment of evidence with respect to the death of David Kelly seems evident, as I read the transcripts of the Hutton Inquiry, Hearing Transcripts.
Consideration of who might have perverted the course of justice in this context is a matter for one or more later posts.