With characteristic cheek, London Mayor Boris Johnson said this morning that he was going to present the US president Barak Obama with an invoice for £5.5m when he arrives in the UK next week.

Boris was quoted on BBC London today as saying “If they are going to have representation in London, they should pay the charge for driving and using our streets. So 'No representation without a congestion charge' is the slogan.”

The US embassy has refused to pay because it says the C-Charge is a tax and not - as Transport for London claims - a charge for a service.

The embassy’s logic is that under the Geneva Convention, diplomats do not pay local taxes. TfL and Boris say the current £10 fee is a charge for a service, loosely defined as clearer roads and reliable journeys in the central zone.

Johnson was also quoted as saying “It is a charge for services and I think we should test this in the courts. The only way we could do this is if the Foreign Office gets a grip on the situation and actually takes the American government to court.”

Once I saw this latter quote, I wonder if Boris is up to his old tricks. It’s my belief that the previous Mayor and Transport for London never risked taking the Americans to court because they feared losing.

Because if the courts did judge the C-Charge to be a tax, then tens of thousands of businesses would not be able to offset the C-Charge as a business expense. You can’t offset tax against tax.

Support (or tolerance) for the C-Charge, or any kind of further tolling of existing roads in the rest of the UK, would collapse completely. Despite Johnson’s enthusiasm for cycling (and his commissioning of the Autocar-inspired range-extender electric bus) I don’t think he would be too upset if the Americans went to court and won.

After all, as critics of the C-Charge point out, what kind of ‘service’ cannot guarantee what it says it is delivering (e.g. free-flowing traffic) and doesn’t refund the money of hapless drivers caught in a jam.