This is always a tricky one isn't it.
I had shoulder pain which was misdiagnosed by my GP as rotator cuff syndrome, which to be fair to him I displayed all the typical symptoms. He was going to refer me to an NHS specialist but because I was in such pain I opted for a speedier route and I plumped to see a 'top' private consultant instead. Who also confirmed it as rotator cuff syndrom and gave me a steroid injection which didn't help at all. It wasn't until I then went back to my GP to ask for an MRI scan that the awful truth was revealed.
Speaking to a young Australian registrar about this, he said it would never have happened in Oz, as soon as I had complained of pain, given my age and the nature of it, they would have done an MRI scan for possible cancer immediately. Different treatment protocols set up to catch problems earlier. GPs need to be trained to watch out for the symptoms and act sooner than they do.
I have to say, once I got past the GP and on to a specialist consultant at UCLH my treatment has been excellent. I do think you have to be proactive though, chasing things up etc. It's important to be an 'active' patient. It's almost like having a job.
I've considered putting a complaint in, but to be honest I've got enough on my plate as it is.
I do sympathise though and good luck with it.
Tom