You've got a helluva good memory, better than mine, but when you mentioned it, it stirred up vague recollections for me of that sensational (for those innocent days) story. On this computer I am unable to post links for some unfathomable reason, but I googled Auster G-AGXT and immediately found a picture with the caption:
"The Auster Autocrat G-agxt That Donald Hume Hired From Elstree Airfield To Dump The Body Of Stanley Setty. The Headless Torso Of Car Dealer Stanley Setty Was Found In The Essex Marshes 1949. Donald Hume A Business Associate Of Setty Was Arrested But ......"
That should give you a starter for 10 for further googling. I also spotted another entry that seemed to say that this venerable aircraft was destroyed in an accident a few years back.
Best of luck in that care home!