The tax is what we used to call 'regressive', that it it falls on rich and poor equally, meaning that inner London travel has been turned into a privilege of the wealthy. Unlike NY, Londoners are overwhelmingly car owners, so there is no sense in which this is redistributive. Indeed current plans are to charge older cars more.
The dubious estimates of the reduction in congestion all pertain to the congestion zone itself without taking into account the increase in congestion immediately outside the zone.
The license plate imaging system is of course fully supported by the police who have been pleased to welcome this extension of their powers of surveillace of the citizenry.
Average speed of London traffic in 1998 was around 11 mph (http://www.dft.gov.uk/162259/162469/221412/221546/226956/coll_trafficspeedsininnerlondon1/trafficspeedsininnerlondon1998)
Average speed in 2006 was 7 mph. (http://www.bikeforall.net/news.php?articleshow=229)
One should bear in mind that it is the official government policy, one that the Greater London Authority has embraced, to INCREASE congestion, which they call 'traffic calming'. Since 1999 local authorities have been empowered to introduce barriers and chicanes with the express purpose of slowing down the traffic (in other words, they have created the problem, and now they are charging us to regulate it).
"The Highways (Traffic Calming) Regulations 1999 2. In these Regulations- * "build-out" means a work for narrowing a carriageway constructed on one side of that carriageway as an extension of or adjacent to the verge, footway or cycle track; * "chicane" means a series of two or more build-outs constructed on alternate sides of the carriageway and not opposite one another; * "gateway" means an object or structure constructed on the verge, footway or cycle track of a highway for the purpose of indicating the presence in a length of highway of traffic calming works of a description prescribed by these Regulations or specially authorised by the Secretary of State or of road humps; * "island" means a work without facilities for pedestrians constructed in a carriageway to reduce carriageway width or to deflect the flow of vehicular traffic; * "overrun area" means an area of carriageway so constructed of textured or coloured material as to appear to narrow that carriageway; * "pinch point" means build-outs constructed on both sides of a carriageway opposite one another; * "rumble device" means a part of the carriageway constructed of material intended to generate noise or vibration in a vehicle passing over it; * "traffic sign" has the same meaning as in section 64 of the Road Traffic Regulation Act 1984(b); and * "20 miles per hour zone" means a zone comprising one or more roads in relation to which the following conditions are satisfied- (a) Part 1 of S.I. 1994/1519, to which there are amendments not relevant to these Regulations. (a) a speed limit of 20 miles per hour applies to each road within the zone; (b) a traffic sign of the size, colour and type shown in diagram 674 of the Traffic Signs Regulations 1994(a) is placed at each entrance to the zone for vehicular traffic."
http://www.opsi.gov.uk/si/si1999/uksi_19991026_en.pdf