Hi Adrian. Your rose is suffering from "dieback". This a rose disease that can be caused by a fungal infection at a wound site or from freeze damage (also cane bores but this does not look like borer damage). The normal treatment is to cut stems back to healthy tissue, but in a bush as damaged as yours, the cure would kill it.

I have had badly dieback damaged roses survive if I just leave them alone, no pruning or fertilizing, just regular watering.

Good luck with your rose. Please let us know what happens.