Ted last year I had a colonoscopy as I developed diverticulitus which without going into too much detail is a cyst which grows out of the colon. I wasn't given much choice as it could have been fatal.
I had, had a year of prior treatment with chemo and radiotherapy for my plasmacytoma and the specialist thought that the combo of drugs had killed off a lot of the good bacteria in my gut and left me vulnerable to infection.
It was a very difficult period and I spent a week and a half in UCLH and took around 3 months to recover.
I can't really offer any advise just this anecdote I'm afraid but the important thing to do is let everyone you come into contact with at the NHS have a complete picture of your condition and any treatment you may have had.
At UCLH I told the gastro surgeon and he liaised with my MM specialist (who also came see me in hospital).