No identification made yet.
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in your related posts, I admit this one is pretty good.
But the lichen itself is not cooperating. It is very immature and these young urban crusts are really not worth the effort.
Probably, they are going to turn into Aspicilia contorta, which is a common, urban, 'chewing gum' lichen on paving stones (and you might even have two subspecies here), but they are simply too young for ID.
By the way, nice Oxalis exilis (Least Yellow Sorrel) at the top of the photograph.
Lat/Lng: 51.4, -0.9
OS grid ref: SU7975