These photos are of the platoon locality at North Warren RSPB reserve (given as platoon locality in 9th Lancs, 42nd Div War Diary - 9th Kings, 55th Div would almost certainly have had a platoon here as well). It is an unusually well developed defence system, with fire trenches, communication trenches, three pillboxes (one of which is destroyed) as well as two probable dug-outs. It has a remarkable similarity to the isolated locality company plan given in the 1925/1936 Field Engineering manuals (Reference - D Sims field work). I hope to expand  more on this later.
The pillbox is a typical 'Suffolk Square'. The damage to the pillbox occurred in 1971. A walker discovered two bombs on June 13th 1971, one of which was broken, and which the finder removed. On June 14th Captain Stewart, R.A.O.C, Colchester attended and found the bomb left in situ to be a white phosphorus mortar bomb. He placed the bomb in the pillbox, and detonated it with plastic explosive, which caused the damage. As a result, Captain Stewart declared that the pillbox would be 'contaminated' with phosphorus for two to three months and as a result the pillbox was boarded up (the remains can still be seen on the entrance and should not be confused with a war-time door/gas curtain fitting!!). Given this is the reserve I work on, I guess I should have posted this a lot earlier!!