Not merely an idiot, in general terms, but , scandal of scandals, not familiar with the byzantine thinking in our defamation law, whereby the burden of proof is put on the defendant , unlike in any other branch of tort. It is extremely rare for a defendant to run the defence of truth,"justification", even though, by any normal standards of evidence and procedure that defence would be perfecty tenable; hence the old saying "the bigger the truth, the bigger the libel".
Whole chapters in books on defamation law are confined to discussing the types of innuendo that may be pleaded: I defy any non-lawyer to understand any of it, and the defamation itself is exclusively the domain of specialist firms of lawyers who do nothing else but grapple with its complexities. That innuendo was found in Mrs Bercow's tweet defies all logic but the logic of the libel lawyer and of the judge, who himself is a specialist libel judge.