Upgrading from Euro III to IV involved a DPF filter being fitted and these were problematic. Euro V was either EGR or ad-blue and was built into the truck from new and as for Euro VI, that is just a whole new ball game; turbo geometry, enhanced electronics, exhaust systems and so on and so forth.
I read somewhere that TFL (I think), said systems will be available in time for the LEZ.
Seen this in a fright in the city email today, commercialmotor.com/news/pr … it-systems
By the look of it non for trucks yet.