Thanks for all the help and advice. I discovered that Black Diamond do replacement middle sections. Only £10 although post and packing added another £8.95. At least it's cheaper than replacing the pair.
Now all I have to worry about is whether it comes from Austria and I have to contribute to the "paying duty on imports" thread
I take the point about safety and the increased likelihood of a future failure. With my luck it would be at a critical point in a descent and I would go flying.
I never used poles at all until I walked the John Muir Trail in California and the Guide encouraged me to try poles with the promise that if I didn't like them I could give them back at the first resupply point point. I got hooked on them and now use them all the time on the mountains. I don't know how my knees would cope now without them.