This is a horrendous situation and disturbing thread to read. My thoughts with Jane, Cat and her family.
Sadly other than potential legal action it's very tough to know what can be done. It is possible to try to raise emergency situation with Ombudsman but that's unlikely to resolve much at the speed needed.
Hopefully the publicity a situation like this can and should get will put pressure on the insurer to review its decision.
1. I don’t often tweet about my personal life, but on 1st November, my mum Jane was hit by a large vehicle as a pedestrian in St. Louis, USA. She suffered a severe brain injury & remains in a coma in hospital.
Here's Jane & me in happier times.