Its diplomats have not paid the daily toll – which is now £8 – since July of last year, racking up a total of 10,486 fines.
Embassy officials claim it is a tax, from which it would be exempt, but London transport chiefs disagree and Mayor Ken Livingstone has threatened court action.
The extent of the dispute was set out in an annual report of unpaid fines and rates by London-based diplomats as well as serious crimes they allegedly committed last year.
It showed the US owed almost twice as much as any other nation's mission in congestion charge penalties – well ahead of Angola and Nigeria which had both failed to pay up more than £500,000. All of the top 10 bar the US were African nations.
The United Arab Emirates paid up nearly £100,000 in outstanding congestion charge fines earlier this year, promising to adhere to the measure in the future.
Two cases of actual bodily harm were among 17 alleged offences that could carry a punishment of a year in jail or more not prosecuted because of diplomatic immunity, the list showed. There were also seven instances of drink driving, one of dangerous driving, six of shoplifting and one of theft of a motor vehicle and driving without insurance.
The latest figures, given to MPs by Mrs Beckett in a written statement, showed embassies owed a total of £332,989.81 in rates – of which they only have to pay six per cent of the usual rate.
Algeria and Zimbabwe were the worst of 12 non-payers, both facing bills of more than £50,000.
There were also 4,383 outstanding parking tickets and minor traffic fines from 2005, totalling £412,530, Mrs Beckett said.
The United Arab Emirates topped the list, owing £42,950 for 441 separate violations.
Liberal Democrat MP Norman Baker said: "It is a disgrace that the outstanding congestion charges unpaid by the US diplomatic mission in London has now topped £1m.
"By what right do they dare to exempt themselves from a perfectly lawful charge that virtually every other country's diplomatic missions comply with?
"This shows yet again the arrogance of the current US administration and the fact that the relationship between the UK and the US is all 'give' by the UK and all 'take' by the US. It is pitiful that the Foreign Secretary can't even get the US to pay the congestion charge."
Mr Livingstone said the US should obey British laws.
"The US Embassy claim that the charge is a tax from which diplomats are exempt," he said.
"They are entitled to their opinion but it is for the British authorities to decide what is a tax and what is not a tax in the UK. Both the UK government and the Greater London Authority consider the congestion charge a charge for a service: reduced congestion."
He added: "The issue here is clear: the US government rightly expects international diplomats living in Washington to respect US law; we are entitled to expect US diplomats living in London to respect British law. British diplomats in the US pay American tolls and charges."