It was in a sorry state and I had to cut lots of dead bits off. I then had to re-pot the poor thing and since that time nothing has happened.
That's when I noticed a new growth. I suppose life in my collection is balancing out. One of my other cacti has decided to give up the ghost. I imagine it's the window positioning. Great for summer, not so great for winter.
I am however, optimistic that I will get the balance right one day.