Some diesels will be exempt from the upcoming changes to what was the congestion charge in London (Feb 08). My wife has one of them. It's also only 35 quid a year road tax.
from
http://cars.uk.msn.com/greenmotoring...mentid=6436135
Free cars include... Citroen C2 1.4 HDi, Fiat Panda MultiJet, Ford Fiesta 1.4/1.6TDCi, Mitsubishi i, Peugeot 207 1.4/1.6 HDi, Renault Clio 1.5 dCi, Toyota Prius, Vauxhall Corsa 1.3 CDTi, VW Polo 1.4 TDI.
Ford is even introducing the a new Fiesta "Sportsvan" with the 1.6 turbodiesel
I have to travel inside the CC zone very occasionally, but since I'm reimbursed, I'll still use my £8 charge car