Insurance is Mandatory

A requirement of the exploration permit is that all team members are covered by adequate insurance.
Insurance details must be passed to the expedition organisers before the expedition takes place.

You will be asked if the area has a local rescue team - the answer is yes...

It is worth checking the small print...
Make sure the insurance covers exploratory caving. Unless explicitly stated, then it won't.
Check for adequate rescue cover. Some policies are so inadequate and they will barely pay for getting the helicopter pilot out of bed.
Worst case is paying for a rescue team camped at the entrance for a couple of weeks plus helicopter transport.

If you aren't registered with a UK doctor, then things might get really difficult.
Miri (from Finland) ended up getting French insurance through an Irish caving club. It was barely adequate, but it was the best she was able to get.