"Just today, there is another large number of relatives with cause to celebrate TB's 'wonderful achievement'". That, to me, suggests that you attribute the full responsibilty to Blair.
"But neither of those things makes any difference to the fact that Blair wanted us in and was prepared to lie to get us in. But going in wasn't the worst part of it. It was thinking that overthrowing the existing regime was all that was needed".
Surely no-one seriously believes that Blair could take a personal decision on the existence of WMD. He took the advice supplied to him by the experts. Most nations believed that Hussein had WMD. There were reports just prior to the time of the invasion of mysterious ship movements, with the suggestion that material had been dumped at sea. So I think you should take the advice of Jeremy Hunt and accept that making statements which may have been false in such circumstances does not amount to lying. And remember that you don't have parliamentary privilege on this matter.
As far as planning for the aftermath, this was a matter for the USA administration and they made many mistakes.