In reply to mmmhumous:
As always, The BMC have been really helpful..... In short the insurance associated with individual membership won't cover you for organising club events.
I've also talked to the BMC's insurance provided to find out how much a it would cost to insure a non affiliated club. They won't insure. which while a pain in the arse, does mean I've persuaded the rest of the club we need to get BMC club membership.