Britain could have left Basra Palace as early as April, but the United States insisted British forces stay on, The Daily Telegraph quoted Brig. James Bashall as saying.
"In April we could have come out and done the transition completely and it would have been the right thing to do, but politics prevented that," Bashall was quoted as saying. "The Americans asked us to stay for longer."
British Prime Minister Gordon Brown's spokesman denied the report.
"The Telegraph story is not correct. The decision to hand over Basra Palace to the Iraqi Security Forces earlier this month was made because the Iraqi Security Forces were ready to take over," spokesman Michael Ellam said.
He said he had "no idea" why Bashall made his statement.
Last week Britain withdrew its troops from Basra Palace, its last base inside the city, moving all its forces to an airport camp on the city's outskirts. Troop numbers are currently being reduced by 500, to 5,000, and Brown is expected to make an announcement on the future of British forces in Iraq next month.
The decision drew scorn from American critics who accused the British of conceding defeat in the south just as the U.S. "surge" strategy is making itself felt elsewhere.
Retired U.S. Army Gen. Jack Keane, who was vice chief of staff when the Iraq war was launched in 2003, said in an interview last month that the U.S. was frustrated with London's disengagement from the area.
Stephen Biddle, a military adviser who counseled U.S. Gen. David Petraeus in 2006, said Britain's Basra withdrawal would come to be seen as a "major blunder in terms of military history." Other U.S. officials hinted that the move could force Americans to divert some soldiers to the south if the Iraqis can't control the Basra area.
Senior British military figures hit back, with retired Gen. Sir Mike Jackson, who led the British army during the Iraq invasion, calling U.S. postwar policy in the country "intellectually bankrupt." Jackson was backed by a chorus of opposition politicians and a second retired general, Maj. Gen. Tim Cross.
Bashall had his own message for Britain's U.S. critics.
"They are not down here, they don't know," he said.