“It’s offensive to me that someone would suggest that I have,” Romney said.

Simmering tensions from the campaign for Florida, where McCain outdueled Romney to win the state’s Republican nomination contest on Tuesday and solidify his front-runner status, spilled over into a crucial debate in California.

Romney, a former Massachusetts governor, accused McCain of lying about his Iraq record. He levelled charges against McCain of holding liberal positions out of step with mainstream Republicans. In response, McCain said Romney raised taxes as governor of Massachusetts and suggested he had changed his position on important issues. Romney said he “absolutely, unequivocally” had never supported setting a time-table for withdrawing from Iraq — a proposition that was a live item for debate a year ago before a US troop build-up began to stabilise parts of the country.

“And by the way, raising it a few days before the Florida primary, when there was very little time for me to correct the record, falls into the kind of dirty tricks that I think Ronald Reagan would’ve found reprehensible,” a tense Romney said, with McCain sitting at his side. McCain, an Arizona senator who backed the Iraq build-up even though it was unpopular, said Romney was asked last year whether the troop “surge” was a good idea and had said, “We don’t want them to lay in the weeds until we leave...”

McCain said he took that to mean Romney backed a timetable for a pullout, prompting an angry denial. “How is it you are the expert on my position when my position has been very clear?,” Romney demanded, saying McCain had multiple chances to bring the issue up during the campaign but had done it only to try to damage him in Florida.