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 ...)