I have Permanent Health Insurance. The good thing is that it covers unable to do your own job (some policies do "unable to do any job", which means they won't pay out if you're capable of doing a job which involves sitting on your arse all day).
I have two policies; one of them pays out after a month of being unfit, and the other pays out after three months. The reason being that the longer waiting period is cheaper cover, as a lot of people get better by then; but if you were to have a long-term problem, that's when you'd really need it because your savings would run out. You can get them with index-linked cover, which is best.
This is better than Critical Illness or Accident insurance, because they only pay up when an insured risk occurs; and even if you're insured for a hundred things, you might get hit by the hundred and first. Also, once you've got it, they can't up your premium just because you've got something wrong with you.
I took mine out when I went into business on my own, I was thinking I might get something terrible like multiple sclerosis.
In fact I was taken ill when driving, collapsed, went off the road, got squashed, was off work for a year. You just never know...
There's a magazine called "Money Management" which IFAs read, but your newsagent can order for you, it has tables of cover and costs per age and occupation. No one company is best for everyone. Both of mine are with non-commission-paying companies, so (1) they're cheap (2) salesmen won't recommend them.
BTW this is about one-fifth the cost of "payment protection insurance" which credit cards and loan companies make a vast profit on, to cover your monthly payments for a while.