Conservative leadership contender Ken Clarke has said Tony Blair made a "catastrophic error" in involving the UK in the war with Iraq.
Mr Clarke voted against going to war in Iraq in 2003
The ex-chancellor, who opposed the war, said the reasons given for the UK supporting the war were "bogus".
The war had increased the threat to the UK from Islamic extremists, he said.
If Mr Blair believed there was no connection between his Iraq policy and the London bombs "he must be the only person left who thinks that", he said.
Mr Clarke also warned against "instant legislation" after terrorist attacks.
"There is no evidence that any bomb has gone off because of any gap in the law," he said.
"Whoever is in power over the next few years is going to find this (tackling the terrorist threat) is going to be number one on their agenda, over and over again," he told journalists at the Foreign Press Association.
"Disengagement from Iraq has to be part of a much larger and more sophisticated political programme than we are delivering at the moment. But this is all part of a much bigger picture."
Mr Clarke referred to his experience serving in a Conservative government tackling the Northern Ireland terrorism threats, speaking of "several Parliamentary colleagues" he lost due to Irish terrorists.
He said the fight against Islamic extremist terrorists should not undermine the "fundamental belief" in the rule of law or give terrorists new grievances which they can exploit.
The government had to be honest about the threat and work with the whole democratic world to tackle the issue.
Mr Clarke said he was keen to "strengthen the alliance" with the US, but added that "US presidents are not always right".
He said the US "failure to prepare" for the consequences of the invasion had led to a "horrifying increase in terrorism".
There should be one independent scrutiny body reporting to parliament on anti-terrorisms powers, including the actions of police and the recent use of the "shoot to protect" policy.
Referring to the Tory leadership battle, the former Tory chancellor said it was his aim make a "serious speech" and open debate among other contenders for what he called "big issues".
"Any future leader of the party or of the country had to be "capable of addressing these big issues," he said, while conceding that his competitors for the Conservative crown were all "very able men".
Also on Thursday, as the Conservative leadership race heats up, rival contender David Cameron interrupted a holiday to make a separate speech.
David Cameron will make a speech on the same day as Mr Clarke
The shadow education secretary called for tax relief to make childcare more affordable to give women more choice in crucial decisions.
His aides say the timing - on the day of Mr Clarke's first major speech - is entirely coincidental.
Mr Clarke earlier dismissed suggestions he was too pro-European and too old, at 65, to replace Michael Howard.
He told the BBC's new political editor Nick Robinson he was "overwhelmingly more popular" than any of his rivals.
This is the Rushcliffe MP's third attempt to win the Tory leadership.
His pro-euro views were blamed for his defeats in 1997 and 2001 but he now says his enthusiasm for UK euro membership has cooled.
As well as Mr Cameron, Mr Clarke's other potential rivals include shadow cabinet ministers David Davis, Liam Fox, Andrew Lansley, Theresa May, Sir Malcolm Rifkind and David Willetts.