Foreign embassies owe £30.4m in unpaid congestion charge fines
Congestion charge dodgers have racked as much as £94.4m in unpaid penalties since the road toll was introduced in central London in 2002.
Figures from Transport for London (TfL) show that of nine million penalties issued up to March 2009, 666,121 fines have gone unpaid.
More than one third of the total is owed by foreign embassies which failed to pay £30.4m in fines up to June.
A TfL spokesperson said "wherever possible, we recover the money owed".
TfL said it had collected 73.3% of the fines imposed.
Over the years it has cancelled 703,257 penalties which were wrongly issued or rejected on appeal.
It classified 941,825 as "aged debt" - where it is deemed too expensive to pursue the debts or impossible to track the drivers.
The TfL spokesperson said: "We have robust procedures in place to ensure that, wherever possible, we recover the money owed through fines while ensuring that the scheme is enforced fairly using a common sense approach."
TfL said it was unable to pursue non-paying diplomats as it was constrained by the Vienna Convention on Diplomatic Relations.
The US Embassy has the highest outstanding payment out of the 128 embassies in London. However TfL said 99 embassies paid the levy regularly.
"TfL and the UK Government are agreed that the congestion charge is a charge for a service and not a tax which means that diplomats are not exempt from payment," the spokesperson said.
"TfL continues to engage directly with those embassies that refuse to pay in order to increase compliance with the scheme by diplomats."
The £8-a-day charge is mandatory for motorists entering central London.