Possibly it's a case of prospective employers wondering what kind of employee they are likely to get, i.e. are you honest and conscientious? And the best way they can judge what you are like is for you to anwer as honestly as you can and tell them what your medical problems are. . Tell them you're thrilled that after three years your health has improved sufficiently to be able to work again and that you're really looking forward to being on somebody's payroll again. . I know of a rehabilitated drug addict who had not worked for three years, but he was honest with a potential employer about his condition, and was given another chance so honesty is the best policy and you will never be looking over your shoulder, once employed, wondering if your secrets will be uncovered. If you don't give permission for a potential employer to contact your GP, they might possibly wonder whether you have the capacity to be evasive or less than truthful in your role as an employee. As you've tried to dodge the issue on two occasions and not had much success, try a different tactic next time and I hope it proves Third Time Lucky for you.