Foreign Secretary William Hague published figures that show the U.S. owes 3.8 million pounds ($5.75 million) after declining to pay a London traffic levy 35,602 times between the introduction of the charge in February 2003 and this January.
Some diplomats claim they shouldn't need to pay the charge as it is a local tax. Under diplomatic rules, embassy officials are exempt from local taxes.
Under the levy, drivers who enter central London during business hours must pay 8 pounds ($12) per day - a policy aimed at reducing congestion on the sometimes gridlocked roads of Britain's capital. The sum is increased if payment is not made immediately.
"The U.S. embassy in London conscientiously abides by all U.K. laws, including paying fines for all traffic violations, such as parking and speeding violations," the embassy said in a statement.
It said it declines to pay the congestion charge under diplomatic rules. "It is a position shared by many other diplomatic missions in London," the embassy said in a statement.
Russia owes the second largest amount with 3.2 million pounds ($4.8) currently outstanding. Japan has failed to pay 2.7 million pounds ($4 million) in levies, according to the Foreign Office figures.
Ex-London Mayor Ken Livingstone once attacked the former U.S. ambassador over his refusal to pay the levy, calling Robert Tuttle "a chiseling little crook."
Boris Johnson, London's current mayor, disputes that foreign missions are exempt from the congestion levy under diplomatic rules. His office said three-quarters of all embassies in London choose to pay the congestion charge fee.
London's transport authorities will continue "to press any nonpaying embassies to live up to their obligations to their host city and pay the charge," Johnson's office said in a statement.
Hague also disclosed that there were 17 allegations of serious criminal offenses made against people with diplomatic immunity in 2009.
Allegations of involvement in human trafficking were made against a Saudi Arabian diplomat and an official at the Sierra Leone embassy. A Saudi Arabian official was accused of sexual assault and an official at the Pakistan High Commission was accused of making a threat to kill, Hague said.
Hague said embassies owed 534,000 pounds ($805,000) in unpaid fines for parking or other minor traffic violations. Kazakhstan has the largest bill - 1,399 outstanding fines totaling 148,000 pounds ($223,000).