Thank you GMC. Snap here - that sort of growth, robustness and sturdiness and no prickles but others have plants with occasional prickly stems.
We were shown a huge old 'Hugo Roller' - said to have been planted in the 1920s. It was in an awkward position on a steep embankment - the upper reach of the flood plain of the Swan River. A gardener had started in on it - decided to give it a 'good prune' and had cut away one side of it and taken that side back to a few stumpy stems. Luckily for the rose, the gardener didn't finish the job and when we saw it, the mass of growth on the unpruned side was completely thornless while the vigorous, soft new growth erupting from the stumpy pruned bits were quite prickly. I wondered whether those prickles were permanent or if they did drop off as the canes aged and hardened. A reminder to get back to see the rose again and check how it's faring.