If anyone wants to know why the Labour party is about to elect Jeremy Corbyn as its leader then they should come and sit in my back garden in Balham.

I have just heard, while lying on a sun lounger, the most absurd and yet horribly revealing conversation between two neighbours talking to each other over the fence.

I think it is worth me giving a full transcript of the dialogue for posterity, so that history might understand why the main opposition party of the United Kingdom elected as its leader a man who signed a Commons motion looking forward to the day when an asteroid hits the earth and wipes out mankind.

It all started with the conversation catching my ear because one of the women was talking about her love of horse-riding. Both women, I must tell you, were middle class, highly educated and very well-to-do.

One of them was opining to the other that she used to be a keen rider, but had not been able to keep it up since moving to the city where she and her husband worked. She now had children and thought it would be wonderful if one day her family could move out of London to live somewhere nice in the countryside with a paddock where they might keep a pony for the kids.

Just an everyday, middle-of-the-road conversation, taking place between two middle-aged, middle-class aspirational mothers, sitting in the gardens of their fairly expensive properties in a south London suburb.

‘I used to be raaaahly into horse-riding. I even did some eventing,’ said the one woman to the other, in a posh voice. ‘Wow! How amaaazing!’ said the other. ‘Yes, but you know how life is? Things took over. I haven’t ridden for ages. But I would like to think one day we might be able to move to the country so the kids can have a pony. Mind you, horses are so expensive.’ And there followed a brief interlude about horse costs, during which I zoned out, because I am always so worried about my own equine overheads that I can never bear to listen to someone else banging on about them.

I lay back in the sun, mind drifting, eyes shut, half hearing such phrases as ‘cost of hay and bedding …hard feed …vet bills and shoeing….’

And then my brain was jolted violently to attention by the horsey woman suddenly saying the strangest and most alarming sentence I have ever overheard. And the sentence was: ‘Isn’t Jeremy Corbyn wonderful?’

‘What the WHAT?!’ I thought, sitting bolt upright. One minute two ladies were talking about ponies for the kids and the next, Jeremy Corbyn was wonderful.

When I closed my eyes in the sun it was to the faint twitter of Middle Britons banging on about their aspirations for little Tallulah and the next thing I knew, I was rudely awakened by the sound of the militant left.

Ponies to Jeremy Corbyn? How is this possible? I tuned back in and it became clear that the women had moved from a discussion of horse costs, via the cost of living, to the state of Britain today. And thence to the issue of how politics was rotten to the core, but no matter because, thank heavens, Jeremy Corbyn would soon be leading the Labour party, of which, by the way, the pair of them were keen members.

Now, I think I told you that during the general election campaign I was made painfully aware of how many of my wealthy, professional south London neighbours were Labour luvvies because a huge number of them put up Vote Labour posters in their front windows.

The ex-builder boyfriend would walk past them screaming blue murder about the hypocrisy of it all. ‘That’s right! Vote for Miliband, you rich morons! I’m voting Conservative because I can’t afford to ruin the economy and not get any roofing work.’

I had an inkling, therefore, that there were many genuine, signed-up Labour members in my street. I had no idea that these were of the renationalising, veganising, asteroid-loving loony left sort. Perhaps the terrifying point is, they might not be.

These might be perfectly ordinary Labour members preparing to vote for Jeremy Corbyn. Or maybe the less terrifying possibility is that all Labour members are renationalising, veganising asteroid-lovers, hurtling towards their own extinction.

Whatever the case, woman two replied: ‘Oh yes! He is wonderful.’ Then woman one said: ‘I just checked I’m still registered to make absolutely sure I can vote for him.’ Woman two: ‘Yes, he’s just what we need. He’s a breath of fresh air.’

At this point, I couldn’t help spluttering. Breath of fresh air? Presumably, the asteroid that hits the earth will be a breath of fresh air too.