Kind of a lucky find. I guess the location should be here:
South England, on the SW Coast Path, looking at Lulworth Castle: Google Maps
First I suspected it to be part of the Maginot line in France so I did a picture search with "france abandoned tank" trying to find one with a similar biome. After some misses I've found one that fit quite nicely.
Quick check on Google Earth showed that the surrounding terrain details like roads, hills and buildings matched pretty good:
Last proof was the little white house in the distance which fits quite well. Also the roof form of the mansion fits.
Perfect!
RIS is usually my first call but with this one I checked it with Overpass Turbo [Landuse=military / military=training_area] which, used with other terrain details, narrows it down quite quickly if you "fly" over the various sites you can line up all the features quickly.
Google Earth even has a decent "street view" from almost exactly where I was standing.
I see this has already been solved - that area would have been my guess too as it's not flat enough to be Salisbury Plain, which is also well littered with tanks! Picture from a bike ride a couple of years ago. I decided not to wander over for a closer look...