As a result of me having lived in London I'm still on the mailing list for Transport for London. I was invited to comment on their consultation for ultra low emissions vehicles. Essentially if you have a diesel car which is not Euro 6, typically registered before Sept 2015 you're to pay £12.50 per day to drive within the Emission Zone. This starts on the 8th April 2019.
The emission zone is enclosed by the North and South Circular Roads. If you drive in the centre of London you'll also attract a £12.50/day Congestion charge. So £25/day pollution/congestion and a £320/day fine if you don't pay the charges.
The charge is unrelated to the mileage you actually drive within the zone, hence is unrelated to the pollution you create or your impact on congestion. In essence it is fund raising disguised in a cloak of EU regulation compliance.
As usual the politicians say you can avoid this by using public transport. This is fine if you live and commute to London, but if you are visiting from the country it makes the whole process a lot more expensive. You could in theory buy a rail ticket to the centre and then use tube/buses, but it is not cheap. I've just checked and an equivalent rail journey for my wife and I tomorrow would be £390 std class return, whereas diesel cost for the same journey by car would be about £50.
You could follow their advice and upgrade your car to Euro 6 which TfL estimate to cost you between £16,000 - £20,000. Helpfully TfL say the Mayor Sadiq Khan will lobby Parliament for a scrappage scheme.
What they need to scrap is this scheme. Not diesels. 100% of these schemes are money generation NOT anti-pollution. If it was pollution then they should be looking at HOME HEATING, that generates 1000's% more than any car. But no the motorist is an easy target for the money grabbers. Glad I no longer have to drive in London/Oxford/etc any more. Back in the 90's the major hassle was paying ££'s for an hour's parking (IF YOU COULD GET A SPACE). Having to visit the major hospitals I eventually gave up and carried my tools & equipment on the train/tube. A hassle but faster and cheaper.