The cost of private health insurance is based on individual circumstances, as you get older the cost goes up , some medical conditions are excluded from cover.
My relative was in the Police for 30 years, back then the Police in N.I. were well paid , him and his wife had BUPA insurance, when he retired the cost of his health insurance went through the roof, so he cancelled it.
Not long after retiring he was diagnosed with Prostate cancer, luckily it was caught early and he survived, it was a long course of treatment which probably cost tens of thousands, if it hadn't been for the NHS he could have in serious financial trouble.