Do you think a Tory PM would've acted differently at the time?
Of course they wouldn't (
https://en.wikipedia.org/wiki/British_Parliamentary_approval_for_the_invasion_of_Iraq)...and then we would be talking about Ian Duncan Smith (or some other failed leader) as the war criminal.
Only 2 Tory MPs voted against action at the time.
Heres' the Hansard transcript of the debate:
https://www.theyworkforyou.com/debates/?id=2003-03-18.760.0
Blair was not alone by any means alone in his thinking - he had consensus across parliament and indeed the EU and UN.
So , much of the Western world should stand trail on the same charges if Blair is guilty as you charge.