I can't help feeling a frustrating sense of dissatisfaction over Alastair Campbell's appearance before the Iraq war inquiry.

Having read the varying accounts of his evidence, it seems to me to have been more of an exercise in flexing his skills as a spin doctor rather than getting to the truth.

It was like Muhammad Ali dancing and weaving around sluggish opponents, landing jabs at will.

He certainly appears to have given a skilled and robust defence of the decision to go to war, using Saddam's removal from power as the justification.

I have sympathy with that argument because Saddam was a brutal dictator. But he's not the only one in the world - so why use force to impose a regime change in Iraq and not other rogue countries?

The answer we were given at the time was that Saddam had weapons of mass destruction capable of being used against us within 45 minutes. That, of course, proved to be untrue and the big question facing Tony Blair in a few weeks is whether he had grounds to believe in advance that the intelligence was questionable.

Without truly solid grounds to believe the WMD threat was real,how could he justify taking the country to war? Surely, a gut instinct that it was right to do so (as suggested by Mr Campbell yesterday) is not enough.

Lib Dem leader Nick Clegg has today called for Gordon Brown to give evidence to the war inquiry ahead of a general election.

It follows Mr Campbell's evidence yesterday that Mr Brown would have been one of the key ministers to be consulted by Mr Blair about Iraq.

That is hardly an earth-shattering revelation. Imagine if the Prime Minister hadn't included his Chancellor in the debate about whether to go to war.

Nevertheless, given the current Prime Minister's involvement in that momentous decision, it seems reasonable to call for Mr Brown to give his evidence to the inquiry before the country votes on whether to prolong his stay in Downing Street.

It is important for us to know what the man who wants to go on leading the country contributed to the thinking behind the invasion, and what lessons he learned in the process.

Who knows? It may be a question he faces again - not as Chancellor but as Prime Minister.