I refuse to answer on the grounds that...

Have you seen the worrying story that your GP is going to be required to divulge information about you - like your  weight, cholesterol level, BMI, pulse rate, alcohol consumption, whether you're a smoker or not and Lord knows what else.  This will all go on a massive database.  We are assured that the information will be used for purely statistical purposes and will be anonymous - yeh, sure, and I just saw a pig fly past the window.  I can understand that in order to get a complete picture they might want dates of birth and post codes, but if they're just interested in the information and not who it comes from, why are they asking for NHS numbers?  I don't know about you, but I shall think twice about what I tell my doctor about my lifestyle in future.  The only saving grace is that large government databases have a track record of failure so it all may come to nothing - but I see it as sinister.