JTD
Only one problem with your theory - as you say "loyalty to the Crown". No one was planning to over throw our Head of State, only the then prime minister. Many believed the then prime minister was a Soviet agent, and without wishing to re-ignite the TSR 2 debate, so was his minister of defence!!!!
The PM is appointed by the Sovereign and it is the prerogative of the Sovereign to remove the PM.
I really doubt that Harold Wilson was a Soviet agent. If he was, he must have been a fairly cr@p one - we kept our nuclear deterrent, stayed in NATO etc....