I doubt the wasps are after flowers, it'll be the berries/fruits causing the trouble. Flowers appear in late spring and summer.

P. henryana may be the answer, as the fruits tend to be small. It may be, too, that the plant isn't the problem, but the sheltered habitat it creates. This year has been really good for wasps (if that's the right way to put it. I've developed an allergic reaction which is a little worrying), and they've made nests of all sizes in all sorts of different places. There may be a nest in the vine somewhere. Phil J

Agree with Phil above, check for a nest, but the vine you have usually only produces fruits after a hot, dry summer, and I think I'm right in saying you in Suffolk have had one of those, like us in London.