BobTheGardener said: It's an Ipomea (common name Morning Glory.) Looks like it might be from seeds of Ipomea 'Black Knight'
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Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
The variety "Grandpa Ott" is similar as well. Mine self-sowed from last year.
I live in west central Scotland - not where that photo is...