HP Victor XL159 lost to deep stall from an intentionally unusual stall entry configuration while with the A&AEE, on the 23 March 62. I’m unsure as to the specific condition being tested but they certainly tried quite a few ideas in an attempt to get it out of the stall. Crew abandoned aircraft, 3 survived, 2 died.
Pilots John Waterton and "Spud" Murphy ejected, the latter at approx 300'. AEO John Tank survived. The other two rear crew were unable to disconnect their personal equipment connectors (a new type) in time and died in the crash. The Victor descended from 10,000' to ground level in approx 50 seconds. "Spud" later became Ops Director for Air Anglia/Air UK (and my boss)