Added a couple of extra shots of the twining / trunk, hoping for a more specific identification.
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We need to see which way it twines to get closer to the species.
Actually, ignore that ID, I think the twining is anti-clockwise. It has to be viewed from above, and I've been fiddling with bits of string to try to copy the twist in your photo. Anti-clockwise twining means Wisteria sinensis, W. brachybotris, or W. frutescens. W. sinesis is the most common.
I'm confident after going back out and looking at it again that the branches are twining clockwise. It's barely twining anywhere, but where it is, tracing the branch from the base of the plant and following it, where it twines it is doing so clockwise from the pov of the base of the plant. So this means it's definately Japanese Wisteria? Or are there still other possibilities? thanks for the help !
You have to look at the twining from above, which I think reverses it and excludes Japanese wisteria - see my earlier comment.
Lat/Lng: 51.8, -2.2
OS grid ref: SO8819