Do you like a lively sound better, or a laidback sound better, OP?
I was in the same situation as you and found some small vintage JBL L-19 speakers here and I'm over the moon with them (but I do prefer a livelier sound myself. although this model seems to be slightly more balanced than other vintage JBL with the typical "west coast" sound).
They have a very detailed sound and great instrument separation and good imaging too, and well balanced across the spectrum. The bass is what surprised me the most : it goes quite low for such a small speaker and has tons of depth and dynamics. I was flabbergasted first time I heard them(and still am) at how powerful(yet controlled) the bass is on these. I run mine on 24 inch stands and the bass is nothing short of thunderous. Yet it doesn't bother downstair neighbours since they're lifted from the floor. I'm running them through a 1975 Pioneer integrated (SA-7500) btw. The Pioneer is a great match for those little JBL.
If you like that type of sound, I say definitely audition the JBL Decade line(L-16, L-26, L-36) or the L-19 or L-50 or L-46. Though I don't know if vintage JBL bookshelf speakers are rare in the UK or not.
I had some super solid Mission speakers at one point (751 mkI) and while I recognised their greatness, I didn't bond with them. Maybe it was my gear(didn't try them on a lot of amps) or my preferences, probs the later. They definitely didn't have great LF extension. They had very nice construction quality though, man those cabinets were heavy! And that tweeter was agile, clear and extended pretty high. Very articulate for sure. I remember the mids were pretty recessed in one area(can't remember if it was low mids or high mids). You are in the Land of Mission so it could be good to audition some, I imagine they're plentyful over there and probably some close to you.
I'll second what another poster said regarding Paradigm : good bang for the buck. I heard a "lower" series (5se) and though they sounded very decent. balanced and clear. nothing outstanding to my ear but nothing offensive either. Would love to hear a higher quality one from them. The "se" series I mentionned is very cheaply had.
And I'll second what another poster said : definitely audition some Braun speakers if you have the chance. I haven't heard ADS/Braun stuff but would love to, considering all the praise I see on here. They seem on the laidback side. Braun should be available for sure in Europe.