Cyclists have every right to be on the towpath, should have a bell and should give way to pedestrians.
Correct. And pedestrians include runners.
Some - not all - cyclists appear to consider speed as the dominant factor in gaining priority, especially on the towpath. And, although the Highway Code only recommends a bell to fitted to all cycles, why do cyclists consider it necessary to ring the bell right behind you: by signaling 20 metres away the sound would be less startling, allow time for the pedestrian (or runner) to move aside and prevent the cyclist from having to brake. Simple.
As a runner I always say thanks to pedestrians, dog-walkers and cyclists; can't say that cyclists do similar to me...