The charge operates on weekdays from 7:00AM to 6:30PM. Electric vehicles and buses are exempt (along with other exemptions).
The system is enforced by ANPR (Automatic Number Plate Recognition) CCTV cameras on all roads entering the zone. Motorists pay by giving their car number plate details at the counter of an appropriate petrol station or shop.
The zone is due to be extended soon, doubling its size.
Needless the say, the scheme is unpopular with motorists, although London has relatively low rates of car ownership in relation to the rest of the UK, or the US.
Plans for similar schemes in other UK cities are currently on hold.
High-profile opponents to the scheme include Madonna and the Evening Standard newspaper.