Single example growing in infrequently managed hedgerow at edge of industrial estate. Looks well established from its condition.
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Check the flowers on different plants. You should find that there are two forms: pin & thrum, like in primroses. Your flower looks like a pin.
University of Edinburgh and Biodiversity Observatory (OU)
Thank you Jonathan; couldn't find it in any reference texts until your pointer; I agree from web-site descriptions of Forsythia that it is the most likely identification. Presumably, it was planted many years ago, as part of the industrial estate "prettification".
The third photo is the leaves of a different plant. It looks like an Hypericum, possibly Hypericum 'Hidcote'.
steve_t; many thanks; third picture removed to avoid confusion. In my original write-up, which I can't see now, I mentioned that the tangle of lower branches made it difficult to be sure that the leaves and flowers were from the same plant. It seems that they weren't.
Found another, smaller, Forsythia about 20m away, but it too had pin flowers. So far, no sign of a plant with thrum flowers, so perhaps not much hope for mini-Forsythias later :-). Will try to remember to re-visit the plant to see if there are any fruits/seeds, once I know what to look for.
If the shrubs were propagated from cuttings from the same bush, then all would be one morph (pin for example).
Lat/Lng: 51.5738, -2.9471
OS grid ref: ST344865
Areas of waste ground between industrial units on the outskirts of Newport, south Wales