Most home insurance policies have both a general "valuables" limit as well as a "per item" limit. £20k would more than likely be more than any limit (but worth checking). More importantly home insurance usually excludes any item used for business purposes, and some would even go as far as saying it invalidates your cover and use it as an excuse not to pay out. If you have a studio at home (that people come to) then many home insurers are funny about that too, just in case someone tries to sue you for injury or the like.
I can't suggest a particular insurer to go to but I would suggest a specific policy would be better as home insurance is unlikey to be sufficient.