An interesting new defence to discriminatory harassment claims has been trialled this month by none other than former London Mayor, Ken Livingstone.

Our Ken was recently appointed to a senior role in Labour’s Defence Review. Objections were heard from a number of quarters including Shadow Defence Minister Kevan Jones on the seemingly not unreasonable grounds that Livingstone appears to him to know nothing about defence.

Livingstone reacted badly, telling the Daily Mirror (why?) that Jones was “obviously very depressed and disturbed”, “might need some psychiatric help” and “should pop off and see his GP” before questioning Livingstone’s defence knowledge.

What makes this an even more puerile rejoinder than it appears at first sight is that Jones has suffered and does suffer from depression and indeed went public in Parliament in 2012 about his struggles with his condition. Despite that public statement and the attention which it created at that time, Livingstone professed not to know that Jones had had mental health issues - though it does seem a curiously specific insult to use if that is the case. Pressed by the BBC on whether his claimed ignorance of Jones’ ill health legitimised his casual allegation of the need for psychiatric help or the deeply condescending “pop off to see his GP”, Livingstone sprang upon a surprised legal world what will inevitably become known as the South London Defence: “I grew up in South London where if someone is rude to you, you are rude back”.

You can imagine the appalled reaction which Livingstone himself (a principal architect of the explosion in race, gender and sexuality training within local government in the 1980s) would have to such a line being used as an excuse for racist or sexist or homophobic remarks. Being from Lambeth does not legitimise what (if said in the workplace) could certainly have been actionable harassment. Shadow Mental Health Minister Luciana Berger weighed in with the opinion that Livingstone’s comments “should be treated as seriously as racism or sexism”, and as a matter of law, that is hard to argue against.

In a further blow to his prospects in a regrettably hypothetical employment tribunal, Livingstone initially refused to apologise. This of course merely compounds the injury to feelings caused to Jones and increases the compensation which might notionally be awarded. And that was despite being expressly instructed to retract the remark by Labour Leader, Jeremy Corbyn, making Livingstone’s “legal position” worse still.

Ultimately, of course, Livingstone did apologise, at least by tweet (one would hope also in person or in writing to Jones direct), saying that Jeremy Corbyn “is right to insist on a more civil politics and as a party we should take this seriously” [obvious subtext - I, Livingstone of Lambeth, do not hold either view].

Let us park the question of whether it is right to allege some mental illness on the part of anyone who raises questions about your competence. Let us leave aside also the predictable hyperbole of distress from around Parliament (“seething”, “fuming”, “appalled”, etc.) and the blatant non-sequitur of Jones’ response that “this is why Ken Livingstone can’t be taken seriously in defence or any other policy issues”. The short point is that no one, and especially not a senior politician of Livingstone’s experience, should conduct workplace arguments by reference to the mental health of others. No doubt on this occasion, Livingstone’s limp and belated apology will be treated as adequate, but it would take little imagination to see how badly that might have played out in a more normal working environment than Parliament.