The United States Ambassador to the UK, Robert Holmes Tuttle, is getting under the skin of London Mayor Ken Livingstone over the city's congestion charge, an £8 (US $15) tax on anyone entering downtown London in an automobile during peak hours. Livingstone now insists that Tuttle owes him more than £1 million (US $2 million) for 10,486 unpaid charges by the ambassador and his staff.

"It's the view of the United States government that all direct taxes on diplomats and diplomatic operations, including this one, are prohibited by the Vienna Convention," embassy spokesman Susan Domowitz told USA Today last year.

Under international law, diplomats pay do not pay foreign taxes. Instead, they pay the taxes of their home country. Livingstone has used the tax to generate hundreds of millions in annual revenue. Last year, before raising the rate, the London tax each day generated £540,000 (US $981,000) in revenue from motorists who paid the charge and an additional £660,000 (US $1.2 million) in late charges and fees for a total of $2.1 million in daily revenue.