AN76 Near Lowerstoft, and further south near Harwich is a good spot for coastal traffic, often submerging there and listening will pick something up. Just got to make sure it doesnt have depth charges on it, in that depth it could be fatal!!
Its defended reasonably well there in that area, the further south you go. But I have sunk several lone merchant ships there between Sept 39 and Jan 1940.
In a type II where fuel is something to worry about AN76 is not far away and you can remain on station for longer. Because I have SH3 Commander I can often pick my patrol square after I have put into any port such as Wilhelmshaven and then move back out to sea within 24hrs after resupply.