Shortly afterwards, reception updated this with a small but vivid amendment. It simply said, 'in Tesco'. My heart sank beneath the ground, enriched as it was with sweat and tears from a morning of people who had said they wouldn't do my job for all the tea in China.

Normally I am far too cheery to agree, but Mrs Stern, who reminds me of my headmistress, was bound to give me a hard time for my inadequacy at her original fitting and I felt a fool. Who could blame her for complaining? I mean, Tesco.

She arrived wearing black and the pessary wrapped in one of those reusable bags that supermarkets are so proud of. 'I won't be using that again,' she said darkly, and I briefly mourned the death of another hectare of rainforest. 'I thought,' quoth she, 'I'd done with pushing things out.'

That was when I first suspected she was not quite as cross as I expected. Indeed it turned out that the loss of the pessary while contemplating toothpaste had startled her into remembering that she had no teeth, so some good had come of it after all.

She mounted my couch like Sir Edmund Hillary on the final step, and I proceeded with a size 74.

'Okay,' I said nervously, 'bear down.' She did, delivering the pessary with the ease of a grand multip on Syntocinon, so we tried again. 77, 80, (I had to retrieve that from the patient loo when she went in there to test it properly), 85 ...

Was there no limit to the elasticity of this woman?

The thing about elasticity though, is that it does have a limit, which we call recoil. At size 90 we found it when, with Concordish acceleration, the ring shot out and pinged across the carpet, setting off my musical Eeyore in the process. Mrs Stern doubled over and clutched her stomach, and I seized her in dismay, fearing vasovagal collapse, or worse.

I need not have feared. She was laughing so much she had split her elastic hosiery. You couldn't make it up.

• You can catch up with Mary's Road to Revalidation blog here