Good point. Maybe those crafty vehicle manufacturers have engineered some built-in obsolescence into the upcoming crop. Still, you almost can drive a top of the range one for peanuts now, perhaps why in general lease prices have increased the last few years.
But that will not stop the second hand market getting flooded with cheap diesel mercs etc. Law of supply and demand. If I can drive a top of the line used merc for peanuts why would I want to drop any money on a new diesel audi even on a lease unless I am living in London and have to.
That article suggests it will only affect diesel cars made before 2015.
My point is these lease deals will get hugely cheaper once the panic sets in as we get nearer to that date so you will miss a chance to pick up a cheap diesel. https://www.theguardian.com/politics/2019/jan/05/london-ultra-low-emission-zone
(I know, that's why I asked him to tell me :) )