Interestingly the Mail has a slightly different slant on why they were buried:
"But the Mark II Spitfires in the secret haul never saw action. Earl Mountbatten issued an order for them to be hidden in 1945 to prevent foreign forces from getting their hands on them as the British army demobilised. The aircraft, straight from the production line, were buried in crates at a depth of 4ft to 6ft to preserve them."