Before I came over to France I used to fish places like that.
There is a stream near Barnsley that goes under the M1 and there is a trout just inside the tunnel that went a touch over 2lbs. I got another one just a bit smaller using a 7' whip from the pound shop. The fish was under a bridge made out of railway sleepers and the rod bent right around it, tip under the water. There is another road bridge very near some fishing ponds where the river runs through a tunnel under the road. There are chub in that tunnel over 3lb. As the stream flows owards the Dearne it runs over gravel shallows no more than 3' wide by 6" deep and there are more dace than water.
The best free grayling fishing in Yorkshire has got to be the River Don running through the industrial heart of Sheffield. There is one stretch that runs between the Trebor factories, a fenced in corridor not much wider than the river itself with factory walls towering above, fork lift trucks running over the bridges and the river is teeming with trout and grayling. Good barbel too.
Urban fishing is much under rated.