THE day Tony Blair gave evidence to the Chilcot Inquiry was bitterly cold.

The world's media had gathered in front of the unprepossessing Queen Elizabeth Centre opposite Westminster Abbey where Sir John Chilcot and his fellow panel members were to hear the former Prime Minister's evidence.

As I toured the various broadcasters' stands, journalists who had been standing about all day clutched cups of tea and did their best to keep warm while off camera.

I said that day that Iraq would be Tony Blair's legacy and his epitaph. Few Prime Ministers have assumed office suspecting they will best be remembered for British military excursions overseas, but it is often the case.

Too often it is, like in the case of Mr Blair and Sir Anthony Eden, for the worst of reasons.

The Chilcot Inquiry has been criticised on many fronts. Sir John Chilcot has, of course, taken far too long to produce his report. It was a greater failing not to have legal counsel.

We did not see the type of forensic questioning of witnesses that we saw during the Leveson Inquiry, for example, with the result that seasoned political veterans such as Mr Blair, Jack Straw and Gordon Brown were able to dissimulate and evade when difficult questions were put to them.

Too often proceedings appeared little more than a platform from which they could present their own version of events.

But there were moments when, simply by giving a voice to those who had previously kept silent, the Chilcot Inquiry uncovered devastating truths and laid them out for all to see.

By peeling away the layers of secrecy which normally protect the workings of the government, the Chilcot Inquiry has shown the strength of the argument being put to Mr Blair in relation particularly to the illegality of the military action he was about to embark upon.

The opinion of the government's own legal advisors was that intervention in Iraq would be illegal without a second UN Security Council resolution.

Yet such was the determination of Mr Blair to follow America into war – telling President George Bush as early as July 2002 "I will be with you, whatever" – that we had the parody of the civil service's political masters dictating exactly what kind of legal advice it would like to receive.

It was fortunate for Mr Blair that the then Attorney General Lord Goldsmith had a more fluid understanding of what international law constituted than some of his colleagues.

The dodgy dossier and the "45 minutes from attack" claims, the diplomatic efforts, the show of support for Hans Blix and his team of weapons inspectors – all can now be seen for what they were: the unedifying sight of a Government attempting to justify itself for a step which, in the words of Robin Cook, had neither international authority nor domestic support.

Mr Blair may have escaped the charge of misleading Parliament but the scathing criticism of his behaviour contained in the Chilcot report is well founded. There was deception by omission: the full facts were not given to the country, the Commons or even the Cabinet.

Apart from Mr Cook and perhaps Clare Short it is hard to see Mr Blair's Cabinet as anything other than badly-informed at best and supine at worst.

There appears to have been little resistance to Mr Blair steamrolling his Cabinet and his party to war. But there was resistance.

The Liberal Democrats, led by Charles Kennedy, were united in opposing the war. Throughout 2002 and early 2003, Charles and I continued to argue intervention in Iraq without a second UN resolution was illegal under international law and that diplomatic efforts as a means of containing Saddam Hussein had not yet been exhausted. Charles spoke out against the war when the majority of the Commons and the country at large supported it. He should be with us today to see his integrity lauded and his arguments vindicated.

The Chilcot report makes clear what many of us already knew: that Mr Blair’s closeness to Mr Bush cost him his perspective.

Clearly Britain's most senior and experienced intelligence officials at the time were also too close to the political machine of government. As the report sets out, there was too much optimism and not enough realism about the quality of the intelligence coming in to the Joint Intelligence Committee.

And just as the spies should have been asking themselves ‘is this enough?’ Mr Blair should have been asking them ‘are you sure?’.

The truth is the intelligence regarding the imminent threat posed by Saddam Hussein – crucial to the legal argument supporting war – was never the reason for going to war nor even an excuse: it was a pretext, stretched and elaborated upon, and one used almost exclusively for the purpose of winning over a cautious public.

The Chilcot report, so long in coming but so extensive in the reach of its criticism, may well give succour to the families of British servicemen and women killed and injured in Iraq.

Sir John Chilcot has said he hopes his report and the light which his inquiry has cast into the workings of the government, the military and the intelligence services will provide lessons for the future.

The shadow cast by Britain's disastrous involvement in the Iraq war is a long one and its failures will dictate British foreign policy for decades to come, in the way it has already affected our approach to intervention in the likes of Libya and Syria.

More importantly, it will serve as a constant reminder of the dangers of the single-minded pursuit of war as a goal in itself.

Lord Campbell of Pittenweem, Sir Menzies Campbell, is former leader of the Liberal Democrats