Insurance is almost irrelevant here, it's more about simple common sense. If you've just had some kind of operation, especially on your legs or arms, then the last thing you should be doing is getting behind the wheel of a 1.5 ton lump of metal and driving at speeds of up to 70mph in it. That's just dangerous to other road users and pedestrians, never mind yourself.
You may think you're fine, but I'm willing to bet the doctor/surgeon knows better and wouldn't have recommended a minimum period you shouldn't drive for without good reason. If you have an accident, your fault or not, who do you think is going to get called as an expert witness is court? And how do you think that's going to look?