Alan, one of the biggest improvements I made was to install room treatments. I would think that in the typical UK room, which is probably on a par sizewise with my very small dedicated room, the same would hold true. IMHO, the smaller the room, the more room treatments become a necessity for good sound.
In the past, like many other a'philes, I too was VERY hesitant to install room treatments before I took the plunge. Why, because not only are they fairly pricey, BUT they have little to no obvious 'gadget' appeal. In the back of my mind, I suspect that was what was holding me back in the past....and which I suspect holds the vast majority of other non-believers back as well. A new piece of gear is one thing, something that has no real tactile appeal, well that's another.
BUT, did I learn my lesson.