When I went into it, I got good deals from Windsor Life and Liverpool Victoria. These two have links to Premium Calculators on their websites, but I just had a look and it really just captures your details so they can contact you
You probably need a Permanent Health Insurance or an Income Replacement Policy if you are self-employed or have no reliable employment benefits such as disability pension and long-term sick-pay.
It is only a reasonable cost if you have a waiting period of 3 or 6 months (so you will only be able to make a claim if you have a really bad accident or illness - which is when you really need it). If you think you might have the odd week off with flu or a bad back you had better tuck away enough savings to cover you.
Cost varies with your age and occupation. It is best to get cover that pays out if you are unable to continue in your own trade (otherwise, if you are stuck in a wheelchair, they might tell you to get an office job)
Once you have a policy in place it will usually be index-linked for benefits and premiums; and the good thing is (on mine) that once you've got the policy, they can't charge you extra or refuse cover for any injuries or illnesses you might develop. If you try to take out a new policy, you will generally not be able to get cover for pre-existing conditions.
You usually get a better deal from a company that does not pay generous commissions to salesmen.