Various ministers (I am not specifically including the PM in this case) in the Labour Governments of the past 10 years (and no doubt the Tory ones before it) have been 'proven' (usually as the result of newspaper investigations/leaks by their staff, etc) to have 'misled parliament' - for which read been caught LYING!! They usually get a slapped wrist, say it wasn't intentional, and carry on as normal.
It is my opinion that the general public's 'perception' (and I choose that word deliberately) is that politicians are like submariners! (How do you tell when a submariner is lying? His lips are moving!!!) Episodes like the Mandelson, Blunkett, Jowell affairs (Cherie Blairs flat 'deal' in Bristol), cash for peerages,Tory sleaze pre 1997 (Archer, etc), all add to this 'perception' and erode the public's respect for the political process, decrease turnout at elections, etc.
While Tony Blair may or may not have lied, and I am not commenting either way, I am sure many of the public today believe (rightly or wrongly) he is as capable of doing so as any other politician!