// I remember distinctly that he was never hounded and hauled before a kangaroo court in order to ascertain whether he was aware that what he was telling parliament was not the whole truth. It never happened. //
In the first place, there's a distinction here to be drawn between what *did* happen and what probably *should* have happened. My point was addressed entirely toward your suggestion that the rules now and then are different. At the very least, in this regard, my point is merely that two wrongs don't make a right.
In the second place, the specific circumstances of the Iraq War seem to have acted to protect Blair from immediate consequences. For example, there's this inquiry from 2003:
https://isc.independent.gov.uk/wp-content/uploads/2021/01/200309_ISC_WMD_Report.pdf
Note that it's the Intelligence and Security Committee, rather than the Privileges Committee, and note that they are careful so say explicitly that they are judging "whether the available intelligence... was adequate and properly assessed, and whether it was accurately reflected in Goverment publications". Still, it's clear that if they found the Intelligence to be obviously inaccurate, and to have been in any case obviously misrepresented, then even back in 2003 Parliament would have been able to draw a clear inference that Blair had lied, and that Blair had lied knowingly.
The problem is, it doesn't. The Report I cite above finds for example that,
// Based on the intelligence and the JIC Assessments that we have seen [prior to 2002], we accept that there was convincing intelligence that Iraq had active chemical,
biological and nuclear programmes and the capability to produce chemical and biological weapons ...
The [24th September, 2002] dossier was founded on the assessments then available.
... the Prime Minister was correct to describe the [February 2003 dossier, aka 'dodgy dossier'] as containing “further intelligence… about the infrastructure of concealment.… It is the intelligence that they [the Agencies] are receiving, and we are passing on to people.”//
The problem, then, is that Parliament in 2003-07 did not know it had been lied to, and indeed actively seemed to agree that it had not been lied to. If it didn't know this, then how could it have agreed to investigate Blair for doing so? It clearly could not have.
In short, then, there was no Parliamentary inquiry into Blair's possibly having knowingly misled the House over Iraq, because the House (or, at least, most of them) didn't even seem to consider the possibility. Clearly, this was a serious failing, and they got it horribly wrong (see also the Hutton Inquiry, which was equally flawed). As it happens, too, some MPs *did* suggest that Blair had misled the House anyway. There just weren't enough of them, and they weren't listened to.