A thick, rather confused web, with very visible entrances. Found at the base of a wall inside a brick tunnel.
No interactions present.
A spider in family Amaurobiidae seems the most likely explanation to me as well, but I don't know spiders and their webs well enough to give a definite confirmation.
Entomologist and biological recorder
I agree with Martin here - if the bluish tinge is real (rather than just an artefact of photography/lighting) this supports it being Amaurobiidae (this colour is seen when the silk is fresh), but it's hard to be certain. The irregular threads are added to each night and if you visit it with a torch, you might be lucky enough to see it happening - when seeking nocturnal invertebrates, I often put a red filter (i.e. a plastic sweet-wrapper) over the torch as this reduces disturbance though it affects the colour you see.
Lat/Lng: 51.6, -0.6
OS grid ref: SU9799