RE: Insurance for instruction (for a mate)...
Check out instructor membership of the BNMAA (british national martial arts association).
This includes insurance cover, provided by Sportscover UK I believe (which is in turn underwritten by lloyds of london if I recall correctly).
I think Sportscover also has a website where you can get an online quote.
Alternatively as said, looking thru the martial arts mags would be a good place to start, but if you do this just be sure that any company you choose is underwritten by a known insurer and registered with the FSA and all that crap.