Parts of it started to die back, and it looked sickly. I thought first that feeding/watering may be the problem as the wall behind it gets very hot, but even after a bad, wet summer it was still dying slowly. One day I stood back and took a good look at it when it hit me - this rose was being treated as a rambler/climber when it was nothing of the sort!
You can see from the picture that the rose has a strong, thick and straight stem, just like a standard rose. I can't think how I missed this for so long. So by allowing it to grow way up (up to the top of the window you can just see in the photo and across under it) it had been stretched beyond its ability to grow successfully. Drastic surgery was necessary, and it required a saw and a good deal of belief that I was right and the plant was vigorous enough to survive.
So I sawed it off about half way up the window frame, above some shoots so that it had leaves to feed itself, and then we waited. Within a couple of months new buds had formed, last year it put on decent growth and produced some flowers. Some light pruning in the autumn and now it is covered in more flowers and buds. It still wants to grow up the wall, so I will need to reshape it later this year as I really want it a bit more compact, but it's healthy and as you can see, producing top quality blooms.
It's always difficult inheriting plants, but the lesson I learned from this is to trust my instincts and make brave decisions even if you don't see the results for a few years. I must confess that I was very relieved when I saw the buds growing, though!