Identified as probably Narcissus 'Carlton'. 2 ids, 3 comments.
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... Narcissus pseudonarcissus sensu lato (trumpet daffodil), as opposed to a short or long cup daffodil, a jonquil, a poet's narcissus, etc. I'm sure that someone else can do better.
There is a downloadable key here that you might find useful, http://www.botanicalkeys.co.uk/flora/content/daffodil.html
Many thanks for your comments lavateraguy and Steve. The key is a great resource.
A daffodil expert has had a look at the photos and says that his impression is that they are of the cultivar Narcissus 'Carlton', a D2 YY with a darker golden trumpet and rather creased petals. It is the commonest of the D2 YY to survive as a garden outcast
He added that usually it is not possible to give a precise determination of cultivars because there may have been back crossing or somatic mutation since the bulb was certified (if indeed it ever was certified).
... D1-YY. Which I guess shows how difficult daffodils are for the non-expert.
Lat/Lng: 57.16, -2.2
OS grid ref: NJ880076