I used to have private health cover with Norwich Union. I never had to use it. Cost wise it really depends on your medical history, age etc. If you already have an ongoing health issue they won't cover you for it usually, or if they do its at a huge cost. Also things like non urgent stuff can add to your cover, it really depends what kind of coverage you want and how *full on*. You'd have to get quotes yourself, as I can't really begin to guess at how much it would cost you.
When I gave it up, they tried to tempt me with all kinds of offers but having spoken to a friend who is a GP I decided to not bother anymore.
Reasoning from her POV is that chances are you will hardly ever need it. You are better putting away the same amount each month in a savings account and then if you need an op and its not happening quick enough on the NHS you can go private and pay for it outright or on a payment plan and use those saved funds to help cover costs.
Working out how much I would have continued to pay in over the years had I kept the insurance and the 2 times since I cancelled my policy that I have opted for private ultrasounds/tests, the insurance would have cost me 4 times the amount the tests did.
I've never worried not having it, but if I did need an op and wanted it done quickly, I'd go private and pay outright or on payment plan. I'd never bother with insurance again.
Of course, if you are getting it via your work then go for it
If they are paying, why not.
Hope that helps