To be honest the ULEZ really only affects diesel car owners in large numbers.
Many petrol cars were compliant long before it was compulsory for.petrol cars to be Euro4, a mate has a 2002 Mini and it is compliant, same goes for a mate with an A4 convertible on an 04 plate, and its a 3.0....
I know a bloke who has a 15 plate E220 diesel and he is going to take a hit when he sells it and another bloke that has a 16 plate Renault van, a Master i think, and its Euro5.
He bought it new and intended to keep it for at least 10 years, now he has to sell it as he can't justify spending nearly £70 a week on ULEZ.
I don't know anybody that thinks Sadiq Khan won't expand the ULEZ as far out as he can.
The cameras and infrastructure for the old LEZ are already in place
If anyone takes a hit on any car/van 10 years old or newer in the current market then it is their own stupidity, even diesels, there are so many selling tools and used car dealers are screaming for new stock, never take the first offer or listen to dealers using the Ulez to push down a trade in price, it is only city drivers affected.
I put my Golf into webuyanycar, first price was 16145, ignored it and it went up every few days, I let them buy it at 18100, I paid 16995 nearly 2 years and 30000 miles ago.
The downside is a replacement will have the same premium.
Your mate with the Renault was mugged, 2016 was the change over to Euro 6, dealers were discounting Euro 5 vans to get out of them, they knew what was coming, the good news is vans are in very short supply and used prices have nearly doubled in the last year or so, finding a Euro 6 replacement may not be so easy.