The two men may have got along famously as they discussed the Middle East crisis at an impromptu gym session on Wednesday.
But clear differences persist in their attitude to policy in the region and, in particular, to the removal of Palestinian leader Yasser Arafat.
Mr Bush is unequivocal in his belief that the Palestinians must get rid of Mr Arafat as the price for a Palestinian state.
'No progress'
Mr Blair has been increasingly strong in his condemnation of the Palestinian leader.
He told a news conference: "I've had 13 different meetings with Chairman Arafat over the past few years.
"But ... you've got a situation where we have not been able to make progress, and there has been an attitude toward terrorism that is inconsistent with the notion of Israel's security."
But in common with the other G8 leaders in Kananaskis, the UK prime minister is still refusing to publicly endorse Mr Bush's call for the removal of Mr Arafat.
Some of these tensions emerged during a joint UK/US press briefing on Wednesday.
Mr Blair looked uncomfortable at times, as his US counterpart outlined his opposition to Mr Arafat and his proposal to use US aid as a lever for change.
This appeared to be the first public disagreement between the two men, even though Mr Blair later insisted there was a "very, very broad measure of agreement" on fundamental goals in the Middle East.
'Poodle' bites back
Mr Blair has been Mr Bush's staunchest ally since the 11 September attacks on the US, pledging to stand "shoulder to shoulder" with the American people.
The UK Prime Minister's unswerving and tireless efforts as an advocate of the US war against terror have led to him being called Mr Bush's "poodle" in sections of the British press.
Those same newspapers are now saying the poodle has bitten back.
The official line from the UK is that the two leader's personal chemistry is so strong it can weather a few disagreements over such issues as steel tariffs or even, conceivably, the removal of Mr Arafat.
'Strong friendship'
The two men certainly seemed as close as ever when they ran into each other by chance at the gym on Wednesday.
"An impressive regime," Mr Bush said of his friend's work-out programme.
"You looked in pretty good shape yourself," Mr Blair replied.
Later, Mr Blair reportedly told Mr Bush that their friendship was strong "partly because you and your colleagues are so open and easy to deal with."
Africa deal
Despite being overshadowed by the Middle East, the G8 leaders managed to reach an agreement on African aid.
Mr Blair had been hoping issue would be at the top of the agenda.
The prime minister's spokesman said he believed the G8 deal was a "significant step forward" in helping Africa.
But it was swiftly condemned by aid agencies who said no new money was involved.
Under the agreement, the G8 leaders will:
But critics will point out the only new money is $1bn a year to relieve debt - half of what Russia is being given to guard and dispose of nuclear weapons.
'Treading water'
A spokesman for the Catholic aid organisation Cafod said the G8 leaders had "failed" Africa and "squandered" their chance to make a difference.
The humanitarian organisation Care said: "This will make for nice headlines but it's not new money."
And Christian Aid said the billion dollar help for heavily indebted countries was at best "treading water".
It said the summit had failed to deal with the fundamental problem of the debt burden of African nation.
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