It's pretty easy to see the cheats. Lorries from 2008 onwards have an additional tank to Carry "ad blue". Pig p*** to you and me.
Dvsa look for lorries older than this as they have to have them retro fitted to get there rfl down. Easy to bolt one to the chassis but not add any pipework and pumps?
Lorries then have euro status, we are on euro 6 now but unscrupulous companies are having chips fitted to euro 4 and 5 to reduce emmsion readings to get lower tax bands saving them bug bucks and of course no cost for ad blue which is now around 80p a litre on top of diesel costs.
The northern Ireland guys are bent as they come, they run every trick in the book. Most firms here run straight 6 engines, the Irish love the V8, they knock the limiters off and often pass me at 65-70 and I'm pretty certain burning zero ad blue.