Two photos - the one showing the bunker was taken about half a mile West of the Norfolk Ornithological Association (NOA) cafe at Thornham. The bunker was exposed to the seaward side for the first time this year. It is probably something connected with the anti-tank range that was in that area in WW2. 
I would suspect that in the next couple of years it might well be found on the beach. The other photo is taken on the seaward side of the pine covered dunes near the cafe. Roughly half of the trees are now dead and gone. Coastal erosion in that area is quickening and for the past couple of years eroded sand from the dunes has covered a prime area for finds of militaria, meaning that finds have been sporadic rather than continuous for me. When I was a boy the dunes were around 50 metres closer to the sea than any are now.
I would suspect that in the next couple of years it might well be found on the beach. The other photo is taken on the seaward side of the pine covered dunes near the cafe. Roughly half of the trees are now dead and gone. Coastal erosion in that area is quickening and for the past couple of years eroded sand from the dunes has covered a prime area for finds of militaria, meaning that finds have been sporadic rather than continuous for me. When I was a boy the dunes were around 50 metres closer to the sea than any are now.