I'm also UK, we are experiencing real cold weather atm this may be one possible cause.
I am not familiar with the pot, the Buddha or the spikey thing in the pot to guess at where you bought this,
I do know many sellers here sell 'piperton' cultivar which is apparently deciduous
If you have this (or one of the other deciduous varieties) there is nothing to worry about
I would recommend asking the seller or checking their website for further information,
How is it doing now? I would advise you to remove all the brown leaves so you can see if the problem is still getting worse. There appears to be new leaves in the pic
If it turns out to be evergreen and or still trying to grow I would advise a grow light, (there are cheap LEDs available on amazon that cost very little to run and will supplement the very little sunlight we get here)
Hope this helps