I think this is a Prunus - plum or bullace or something like that
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Yes quite likely prunus but you'll need to keep an eye on flowers, leaves and most important fruit as some of these look very similar.
I think the buds on this are too big for blackthorn and the thorns lack the er.. 'knobbly bits' that blackthorn shows see this http://www.flickr.com/photos/hammo114/5354343974/in/photostream/
Obviously, flowers, fruits and leaves would help!
We could have images of two trees here as the twig showing buds has no thorns.
It could be Hawthorn plus something else.
You're right that these shots are from different trees, but I think they are the same species. Maybe they are blackthorn after all - will certainly check the flowers and leaves when they appear!
I will go for Hawthorn and a possible Cherry Plum.
Lat/Lng: 52.8, 1.3
OS grid ref: TG2529