The leaves on the Clematises I googled look a different shape, Cotoneaster looks the nearest in leaf shape but mine isn't glossy. It is behaving like a fig, growing over the tops off other trees, clinging and climbing yy Helly. In East London, Oaty, so not particularly warm & frost-free! Neighbours not sure but a horticulturalist lived here about 3 people before us, so could be anything. Garden has definitely been landscaped, has a date palm & a couple of big yuccas.