Kev, "Still couldn't trust a fart though". Yes, that was my problem too, happily things are now slowly improving three and a bit weeks later. I was worried the radiotherapy had done for the sensory nerves near the anus (the ones that distinguish between gas and poo) but it may just be that radiotherapy had caused inflammation such that every nerve signal was equally sensitive.
Anyway, as I said above dietary fibre hasn't been the cause of problems. Interestingly though, although I haven't had urinary symptoms generally I am much more sensitive to caffeinated coffee than I have been for several years (I had surgery in 2016).