For what it's worth, no matter what the underlying soil is, a century of decomposition of turf thatch will develop a layer of humus. If wet, it will compact, and we all know that compacted soils A) don't drain freely and B) are difficult conditions to keep a quality sward of turf. From the picture of the gravel layer exposed by the bunker, I wouldn't expect a sand layer above, it look like a glacial aluvial outwash.
In much of the States, courses are on clay-loam and require routine aerification to punch through compacted layers to allow roots to grow deep. We also know that short, shallow roots prevalent in compacted soils will crap out in hot, draughty weather. I have never been to Addington, I can't speak from experience, but, from the posts, it sounds the course could use some agronomic help. Breaking through the hardpan to allow access to the gravel would help drainage. Also, if the growing medium above the gravel is thin, it could lead to draughty condition if, as reported, there is no supplimental irrigation available.