Revealing mistake: When Mellish is stabbed, there's already a hole in his shirt before he's stabbed.
Revealing mistake: If you look at the river under the bridge and all other shoots it isn't flowing yet it is quite shallow. In one shot the wind is blowing the surface.The river was purpose built along with the town on former British Aerospace Factory in Hatfield Herts and the river is a shallow oblong mini lake the runs the width of the set.






Answer: These were barrage balloons, commonly used during the war. They are used to stop low level bombing and low level fly bys by enemy fighter planes. The cables attached to the balloons are designed to cut through the wings of the aircraft and to bring them down, so any pilot would have to fly above them, and the balloons would also restrict the view from above.