Go private again and see a different specialist. The specialist I saw offering me reassurance that he was confident I don't have bowel cancer he rushed through my colonoscopy on the nhs so I didn't have to pay for it privately. 
he reccomended that I don't do a fit test so straight to the colonoscopy. My father also never had to do a fit test straight to the colonoscopy. 
I think fit tests are quite accurate but if you have symptoms they shouldn't be ignoring you x

Thanks for.the reply. I paid £200 for 20 minutes and he simply repeated my NHS history of tests. Astonished....just need to spend anotherq 200 bexuase of 18 month waiting in my area..Good luck.