The brainchild of Ken Livingstone and the metropolitan equivalent of the (soon to be implemented) national Road Charging scheme, the Congestion Charge is roughly confined to central London at the moment - though several cities are chomping at the bit to swell their already bloated coffers with yet more easy money squeezed out of the supine public cash cow.
It works like this: 150 miles above the Earth's surface, a string of hunter/killer satellites monitor every single vehicle entering and leaving the city's electronic boundaries. A chip - embedded in the driver's brain - monitors heart rate, sperm count and blood pressure (which is linked in to the traffic light system) and automatically triggers a direct debit from the hapless driver's bank account.
Each time a vehicle crosses the invisible electronic frontier, the council's slush fund increases by an astonishing £27 billion EVERY SECOND. This is then squandered on fact-finding trips to the Cayman Islands, diversity awareness schemes and puppet theatres for disabled Nigerian lezzers; instead of using it to fund the 2012 Olympics that the bloody taxpayer will inevitably shoulder the cost for. Money well spent!
However, there are some vehicles that are excused the Congestion Charge for various good & Green reasons. These include electric cars like the Toyota Prius, and buses/minibuses. This can be dashed handy for those who forgot to buy congestion charge tickets before invading Central London in a white fleet parade of drunken debauchery, or owners of Landrover Defender Safari waggons, which have 11 seats and are therefore exempt the charge. It gives one a warm glow to drive a 4x4 into the heart of Ken's domain and not have to shell out the ackers.