Here's a juxtaposition. One the one hand, Tony Blair's partial apology for the Iraq war has reminded us of the greatest failure of New Labour whilst on the other hand, Speri's Tony Payne reminds us that Blair delivered "many substantial achievements" - among them the reduction in pensioner poverty, decent productivity growth and introduction of tax credits.

But what, if any, was the relationship between the two? Was Blair really a split personality PM, being good if limited Dr Jekyll in domestic policy and evil warmongering Mr Hyde in foreign policy?

I suspect not. Here's a theory. Some of the thought processes that took Blair to war were also processes which underlay his thinking about domestic policy. I mean this in four ways:

- An excessive faith in the "intelligence" that told him that Saddam was a threat. This represented a failure to see that knowledge is often severely limited. There's a counterpart to this in domestic policy: the belief that public services can be managed by targets also rested upon a belief that fragmentary dispersed and partial knowledge can be known to a single mind.

- Leadershipitis. A feature of New Labour was a faith in leadership and bosses. Peter Hennessy has described Blair as a "command and control premier" who believed that "you either have a strong and determined approach to the job or, just like that, you have weakness, indecision and chaos.*" This belief in the importance of leaders led to the idea that deposing a bad leader was sufficient to transform Iraq for the better. In both cases, there was a failure to see the limits of leadership and importance of complexity.

- Modernity. "If there is a single word that might capture the essence of Labour's social and political project then it is 'modernization'" wrote Alan Finlayson. Blair seemed to believe in a simple linear view of history in which modernity was both self-evident and good. I suspect he had a similar attitude to Iraq: he thought removing a dictator would turn the country into a "modern" liberal democracy. Sadly, it wasn't that simple.

- Deference. Blair was excessively deferential to those in power - both to President Bush and to military intelligence.

In these senses, the Iraq disaster did not arise from Blair having a personality change. Instead, it was the result of the same ideology he applied to domestic policy - a faith in hierarchy and neglect of the importance of complexity. This ideology also contributed to his some of his domestic failures - such as the failure to increase public sector productivity (pdf) and to restrain the rising power and wealth of the 1%.

In saying this, I don't intend to deny that there were also, as Tony says, significant achievements. And, indeed, these arose in part from the same ideology that yielded failures: without that simplistic faith in "modernity" Blair would not have made Labour so (temporarily!) electable. Strengths and weaknesses are often the same things applied in different contexts .

* "Tony Blair as Prime Minister" in Chadwick and Hefferan, The New Labour Reader.