If you read a thread called "The Scene is Set" you might get an inkling!
Some landowners are not to happy to have a helicopter land without prior permission and the MoD are the worst (in my experience)!
The pilot did the absolute safest thing in returning to base; there may be problems with disused pad that he or ATC wouldn't have known about and he probably didn't want to find out the hard way!
Cheers
Whirls