Hi Nancy
I work in the UK in the insurance business!!!! It might be a bit different over here, but if you apply for medical cover for the first time, you will be underwritten and certain things would be excluded from the policy, or a moratorium applied. However, once you have been accepted they are permanent covers, and the insurer is obliged to keep you on as long as you continue to pay the premiums. Premiums go up each year due to medical claims inflation, and they are morbidity rated.
However, in UK it might be possible to transfer from one provider to another on a protected underwriting basis, meaning that the new insurer buys the business in but cannot underwrite the applicant again. We did this a few years ago when we changed provider.
It does not surprise me that any potential provider would make such restrictions, as we are more likely to have further problems as we get older. Remember they are not charities!!!!