David Cameron has denied the Government performed a U-turn by freezing fuel duty after Labour called the move "another case of panic at the pumps".
At Prime Minister's Questions, Labour leader Ed Miliband claimed stopping the 3p increase planned for August was proof that "Plan A was not working".
But Mr Cameron insisted the coalition was "defusing Labour's tax bombshell" and that he was proud of the change, which was announced on Tuesday.
He told MPs: "The fuel duty increase was a Labour tax rise. It cannot be a U-turn to get rid of a Labour tax increase. They put in place 12 increases on fuel duty in government. They left behind six increases in fuel duty and I'm proud of the fact we are dealing with them."
Downing Street indicated earlier that Government ministers had not been told in advance about George Osborne's £550m decision to suspend the 3p hike in fuel duty.
His announcement during Treasury Questions caused astonishment, coming just a day after Transport Secretary Justine Greening publicly defended the hike.
And as recently as last week, Mr Cameron appeared to pour cold water on motorists' hopes of a rethink, saying the planned rise would be "looked at" but adding the Government "doesn't have a bottomless pit of money".
Mocking the Prime Minister at their weekly clash, Mr Miliband questioned why he had forgotten to tell the rest of the Cabinet and the party's backbenchers about the plan.
"So it was all part of a seamless political strategy?" the Labour leader said.
Speculation the Chancellor might not have warned his colleagues was sparked when junior Treasury minister Chloe Smith repeatedly refused to say on BBC's Newsnight when she was told.
Outspoken Tory backbencher Nadine Dorries called the Chancellor a "coward" for putting up Ms Smith to defend the policy shift on the TV show.
She wrote on Twitter: "If Osborne sent Chloe on re scrapping 3p he is a coward as well as arrogant."
Referring to regular backbench grumbles that Mr Osborne does not put himself on the front line to fight the Government's case in the media, Ms Dorries added: "The submarine Chancellor sacrifices another minister whilst he slips under the surface... again."
In the Commons, Mr Miliband seized on the tweet, telling the Prime Minister it was "no wonder" Miss Dorries had called the Chancellor a coward.
"The Chancellor hid away yesterday, refusing to defend the decision," he said. "The Chancellor yesterday sent out the economic secretary to do interviews on this issue."
