Its worth remembering that the UK and USA have very different laws regarding waivers with combat sport. In one country they are worth more than the other.
All legit clubs should have blanket public liability, public indemnity insurance including member to member accidents and instructor liabilities. Our insurance covers us for several million. That said we don't let guys on their free class spar, so they have to have signed up to spar, and we also recommend that they have at least 6 classes and watch as much sparring as possible so they know what to expect. That said if someone gets hurt sparring, well its sparring.. The main thing is we cover ourselves by having proper insurance and doing everything that can be reasonably expected in the event of a mishap.