This may be apples and oranges being that I'm in America, but I have a 'valuable personal property' insurance policy for my musical instruments. For instruments in the few-thousand-dollar range like my Morse concertinas and my Martin guitar, the insurance agency just accepts my personal appraisal. For the Jeffries, I got it appraised professionally and faxed the appraisal letter to my insurance company. I think I pay $100-200/year total for all the instruments (about $20,000 total appraised value for eight or ten itemized instruments?), and they're covered whether I'm home or traveling. I don't know whether the policy would have to change if I were using them professionally.
Lower-value possessions have just been included in my home-owners (or previously renters) insurance policies, whether I and the possessions are at my dwelling or elsewhere. I don't know where the line officially is between 'a normal possession' and 'valuable personal property'. My laptop costs more than my Pokerworks, but the laptop is just 'a normal possession' while the Pokerworks are also in my VPP policy. (But I added them as sort of an afterthought and maybe I didn't really need to.)
Things may work entirely differently in the UK. I'm curious.