could be damage from vine weevils.

difficult to find the culprits and i'd avoid using insecticidal sprays.

Leaf-cutter bees, they use the leaves to make a nest. Look at it as part of nature and helping to look after the bees and should not "be controlled or stopped"
https://www.rhs.org.uk/biodiversity/leaf-cutting-bees

I would agree with Eileen and go for vine weevils. If you go out when it gets dark with a torch you can see them on the shrub. Just place a container underneath and flick them off. But beware, neighbours might think you are mad or up to no good at that time of the night.

Thank you very much. I did venture out last night and found some vine weevils not on the rose but up high on my sunflower leaves. I flicked them off but forgot the container!. When I do it again and catch them please could you let me know what do I do with them and is there anything more I can do to stop the others?

For a start, when you catch them, just squidge them. I would continue with the nightime expedition. If anything that's grown in a container suffers from vine weevil you can treat them with Vine Weevil Killer. Anything grown in the open can be treated with nematodes. These can be very expensive and when the nematodes have finished off all the vine weevils they will die. If you think that only your sunflowers are affected, then I wouldn't grow them in future.

Thank you very much - they’re on the rose as well judging by the bites out of the leaves but obviously didn’t fancy them last night!

They make a very satisfying crunch when stood on. Never found a chemical treatment that will kill the adults by the way. Once had one swimming in pure bleach overnight and it was still alive. Come the end of the world, them and cockroaches will be the only survivors.