Welcome to the world of bonsai.
Your Chinese elm is probably looking a bit sad because it has been inside where there's not enough light, humidity, etc.
It may also be sensing the approach of winter and preparing to drop leaves for dormancy.
A third possibility is overwatering. Beginners tend to keep the soil wet which can actually kill roots, especially where the soil is very fine and compacted.
Good news is that they are also very hardy and resilient so it should recover if given better conditions.
Best outside, probably with plenty of direct sun. Full sun in UK should be fine but the tree should still be OK with some shade if that's all you can provide.
Chinese elm are hardy enough to manage any low temps the UK weather is likely to throw at it so no need for winter protection unless you live somewhere super cold.
Repot before the leaves open in spring but Chinese elm is hardy enough to cope with root pruning even after leaves have opened.
Hard to tell from the picture angle but looks like some of the branches might be growing in strange directions? Cut off any unwanted or wayward branches to refine branching arrangement and to maintain the desired size and shape.
