Efforts to force foreign tourists to pay London's congestion charge look set to be thwarted by overseas law, which will prevent debt collectors from tracing drivers in many countries including Germany and Denmark.
The mayor, Ken Livingstone, last week signed a deal with Europe's biggest debt collection agency, Intrum Justitia, for an enforcement network covering 21 countries.
But Intrum Justitia's UK managing director, John Easden, has admitted that coverage will be distinctly patchy, as some foreign governments will not cooperate.
Germans and Danes will be able to drive free of charge through London virtually free, as Intrum Justitia has no means of identifying them from their number plates.
In France the cost of obtaining registration details is so high that Intrum Justitia will only bother chasing serial offenders. "We can only go by local laws," Mr Easden said.
"We will try to trace the registered keepers from the local equivalent of the DVLA but we can only do that where it's permissable. In Germany, we couldn't trace a person based on finding their number plate. In France it's a bit different - the cost of doing it is more than the penalty notice."
The £5-a-day charge will be policed by hundreds of cameras, which will take pictures of number plates and compare them to a list of vehicles which have paid.
Those refusing to pay will face a penalty charge of £80, rising to £120 after 28 days. Transport for London pointed out that even if drivers came from countries where their cars were untraceable, the authority had the power to clamp, tow and crush vehicles with a record of non-payment.
Foreign visitors could significantly contribute to the "refusal rate" of the charge. According to the London Tourist Board, more than 863,000 Germans and 1.09 million French people visited the capital during 2001.
Intrum Justitia said it could vigorously pursue visitors from some countries - including Belgium, Italy, and the Netherlands. But there are no plans to pursue vehicles from outside Europe, as the number is considered insignificantly low.
