Sorry to hear about your misfortune Monty.
Tradesmen who work on a sub contracting basis for kitchen companies are required to have public liability insurance and a licence from the Dept. Fair Trading.
You are lucky that the kitchen company states in writing that they will accept responsibility for the sub contractors actions.
If you dont have any luck, you should first seek advice from the CTTT (Consumer, Trader & Tenancy Tribunal) through your Dept. Fair Trading office.
Hope this helps you Monty.