Tube-Curious/Pre-amp

Why not look into hybrid integrated amps?  You could sell or trade your Atoll in.  I had a pair of bridged Pathos Classic One MK III's a few years ago that were quite nice and before that miscellaneous Chinese amps, Xindak and Consonace.  Soundwise, all were nice but reliability issues would preclude a recommendation on those Sino-amps.  And being in the UK, you have access to all of Europe and a better exchange rate.  Go to hifishark and type in "hybrid integrated" , both for sale and those already sold, for several possibilities

Icon Audio LA4? It’s local to you as well. 

This should do the trick 

I saw someone mentioned a Dared. If you can find a used Dared SL2000a I'd say it is a great true tube preamp if you are wanting to get your feet wet. They are sensitive to tube rolling so you can get a few different flavors out of it. Runs off a 5z4g rectifier or equivalent and a pair of 12at7's. It is so sensitive to tubes even the rectifier you choose will make a big difference. Only 2 inputs but has 2 outputs as well. Good internal components like Rubycons, auricaps, silver wiring inside..although some later models had different coupling caps than the auricaps, they sounded just as quiet and transparent though. They are of Chi-Fi nature but reliability was never an issue, mines over 12 years old and I still use it on occasion with no problems. I use an integrated amp mostly these days but I'll run the Dared thru the HT bypass when I'm in the mood for certain genres of music and want that little extra realism or roundness to the instruments. 

They don't pop up on the 2nd hand market much but when they do they usually go between 3 and $500. A lot of good preamps mentioned in this thread but with you saying you just wanna try out some tube sound I would go used and cheap if you can find a decent one..or I guess you could try new from a U.S. company if you can get a 30 or 60 day return policy. Just thought I'd give Dared a 2nd mention on the thread, I even had one of their "cheap" tube amps a long time ago..I had no complaints. 

They do have other tube preamps and amps to look at, some cheaper than others,  but I think the SL2000a is a great cheap, very quiet, tube preamp. I run mine thru an Arcam SA30 which is pretty quiet and transparent, with the tube pre it's still the same, just adds a little roundness to the instruments. Good luck, seems like a lot of good gear was brought up by members here. 

Wow, thanks for all the time spent replying to my OP, genuinely appreciated. I think I need to do more reading and research - lots of brands suggested I had no previous awareness of.

First decision I think will be pre-amp, or additional tube integrated and take it from there. Lots of time over Christmas 🎄😊

Thanks again everyone, and I hope you, and all your loved ones have a great Holiday. 

Much appeciated

L