That's true, Stubax, and all current production models have to fully comply with Euro 5 as of January 2021. I expect the UK will retain the regulations which are used by many of the countries of the world, including Japan. However there are technologies such as variable valve timing (used on some of their machines by BMW, Ducati, and Suzuki) which is very effective at controlling emissions without need for major modification. Could Honda do it by removing the Vtec and using ride by wire on the V4? Possibly so but they would probably dismiss the idea due to the age of the engine.