‘Oh, it was fine. I’m just so tired that I can’t move. You know what it’s like when you start a new job – you’ve got so much stuff to remember and your brain gets overloaded. I could literally fall asleep here.’

‘That’s not a good idea,’ she says, briskly. ‘We’re supposed to be going to Pilates, remember?’

‘Oh my God. I can’t.’

‘It’ll be good for you.’

‘I don’t want to engage my core and strengthen my glutes. I want to lie on the sofa with a tub of Ben and Jerry’s and watch crap on TV.’

‘You can do that afterwards. It’s not on until nine.’

‘You know what I mean.’

She hooks me under the elbow and tugs me up to standing. ‘Come on, I’m not going on my own. Last time I did that creepy Charles tried to hit on me afterwards.’

‘FINE,’ I say, yawning so hard my jaw cracks.

The thing about living in Notting Hill is that even the most basic gym class is super posh. There’s a string of black Range Rovers parked outside the fitness studio, and inside everyone’s Lululemoned from head to toe. I’m in a bog-standard pair of sports leggings from JD Sports and a vest top, so I hide at the back of the room so nobody notices me, taking a yoga mat and parking myself in the corner beside a young mum who has a sleeping baby in a carrier. Becky’s standing at the door answering a last-minute call when the instructor walks in.

‘Hello, everyone.’ She’s a cheerful looking Australian woman of about forty-five, with the figure of an eighteen-year-old. Her buttocks are so perky that they look like they need their own morning TV show. She tosses her water bottle to the side of the room and claps her hands. Her ponytail swings. Oh God, I think, this is shaping up to be a torture session.

‘Now then,’ she says, giving me a welcoming smile. ‘We’re going to shake things up slightly this evening, for those of you who like to hide in the corners. Pull your mats back a couple of feet.’

Everyone does as they’re told. There’s a very quiet murmur of dissent, but nobody’s brave enough to speak up.

‘Excellent. So the back row is now the front row, and the front row is the back.’ She looks very pleased with herself.

I don’t know who’s more disappointed – the Lycra-clad goddesses who like to show off in front of everyone, or the scruffy reprobates like me who are now centre stage. I’m pretty certain my knickers have gone up my bum and now I can’t hoick them back out.

I haven’t been to a gym class since school, when Miss Bates the terrifying PE teacher used to make us do yoga with a side order of military-style barked instructions. Now I’m standing beside my mat wondering what exactly I’m expected to do.