Pollution Study in Commuters, Test subjects required

I think London is also a bit special that it effectively removed all modern engines from central areas
with the congestion charge. All that's left are old style diesel engines in buses, taxis and lorries.
The Vans are probably the only ones that might have modern filters.

Eh? So, er, none of the cars we see day to day in central London have modern engines. Hybrids, electric cars, and low-emission vehicles are removed by the congestion charge despite the fact they're exempt. The low emission zone and its daily charges for particularly polluting commercial vehicles has been completely ineffective and only old-style diesels are left.

Glad we've got that cleared up then.

(Or maybe you've got a bit of a special take on reality, just maybe ...)

jsabine is right. Previous efforts to introduce a Lower Emission Zone (LEZ) in Central London are currently completely dead. The Congestion Charge is less effective than it was at first as the charge hasn't gone up with inflation, and the Western Extension, the first segment of a putative larger, 'doughnut' zone around the original zone, was abolished by the current Mayor. You can therefore expect all kinds of motor vehicles in Central London (of which much of the area of the Western Extension is a part).

Towards the end of his mayoralty, Livingstone introduced a lack of clarity into what he wanted to do with these zones when he started to expand its remit to lowering emissions. This confused a lot of people and the public narrative that was meant to justify them weakened. In the meantime, technology has moved on and there is actually no real necessity to introduce those fixed zone boundaries. The current problem is that the availability of different options has paralysed decision-making around the issues. There is also a strong story about how these measures are gimmicky and not comprehensive enough to transform London.