Hey there!
So, I have the V3 map, I haven’t upgraded to V4 yet. But I do know that the V4 map differs in some ways from the V2 map. I can’t remember specifically all of the changes, but there’s more territories now. There’s an extra territory each in England and Japan I know for sure, for example. and I believe an added territory in Norway as well. So while not a ton of changes, there are some that I believe affect the initial setup. I’m sure you could tweak a bit though to make it work if needed. And of course there’s the added terrain features as you mention. Funny you mention not liking the jungle terrain, I specifically bought the V3 map at the time because I wanted the added terrain features!
It’s been a couple years now, so I can’t remember our specifics, but I remember us using our V2 map and using the V3 rules and we just tweaked some set up and/or rules as needed to make it playable before we pulled the trigger on buying the V3 map.
Hope that helps! And I hope you find some UK players!