GPs are gatekeeping hospital resources. They are keeping hospital services from being over run by those pesky 'worried well' people. Who can in fact be quite hard to tell from actually ill people!
This is the problem Mamadoc, they are not always terribly good at this and can become very fixed in their mindset that someone is neurotic or hypochodrial rather than ill. This means that they don't refer for further testing.
Three people in my family (including me) have had cancer missed by a GP, in 3 different practices, in 3 differents parts of the country. We asked to meet with the GP who misdiagnosed my uncle's brain tumour as high blood pressure - we didn't want to sue, just to understand how it all happened, and were basically told to leave and "never darken his door again". My own misdiagnosis was horrific - despite the fact that I had every bowel cancer symptom going, the GP decided I was hypochondrial and said that the only referral I would get from him was to the mental health team.
I only got treatment when the tumour ruptured the wall of my bowel and I collapsed with the pain. Result - I had a much more major operation than would have been necessary had my GP not been a twat and yes I did sue in the end
Obviously 3 cases is statistically insignificant, but this seems to be happening all over the UK. Having since married an oncologist, I know that he sees many, many similar cases. I have no idea whether it is resources, poor training, overwork, or what, but it seems to be a shit way to run primary care.