From what I can see (though image is a little blurry) I would say it's one of our Cave spiders, Meta sp.
We have two large species of Meta, Meta menardi and Meta bourneti. Neither are commonly recorded but the latter species is the more rare. They are Troglophiles, cave loving species, and live only in very dark un disturbed places. This includes caves, undisturbed cellars and underground drains and culverts.
They are a large and impressive species but are harmless.