The "testament of MI5 agent Alex Gordon" was certainly not "damning evidence" of Wheeldon's guilt. "Alex Gordon" (real name: William Rickard) was a mentally unstable journalist with a criminal record who was employed by PMS2 as an agent provocateur. His deranged imagination produced the allegation that Wheeldon and her family planned to shoot Lloyd George with a poisoned air-gun pellet while he was playing golf.
Although Rickard's evidence was central to the Wheeldon trial he never appeared in court to face cross-examination. PMS2 later packed him off to South Africa to get him out of the way and he eventually committed himself to a mental asylum.