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.