Just to add to the fraught atmosphere, Tilda and Toby had a massive shouting match last night. I could hear them through the wall and it made me wince. (I also decided it would be tactless for me to pop straight round and say, ‘Oh, Toby, you’re in, did you get my email?’ So I left it half an hour and by then he’d gone out again. Typical.)

I know it’s tough for Toby and that his generation have it hard. I know all that. But I think Tilda’s going to have to be firm. He needs to get a job. A place to live. A life, basically.

I’m actually quite apprehensive as I knock on her door on Thursday evening, in case I come across her and Toby mid-row again. But as she opens the door she looks quite calm – mellow, even, and there’s music playing in the background.

‘He’s out,’ she says succinctly. ‘Staying over with friends. We’re fine. All ready?’

‘I guess!’ I give a nervous laugh. ‘Ready as I ever will be.’

‘And Dan?’ She peers round to next door, as though he might suddenly pop up.

‘He thinks I’m at book group.’ I grin. ‘You might have to bullshit about our interesting discussion on Flaubert.’

‘Flaubert!’ She gives a short laugh. ‘Well come on in, Madame Bovary.’

I’ve been googling ‘boudoir photos’ pretty solidly over the last three days, and as a result, I’m equipped. More than equipped. I have procured: a spray tan, a manicure, a pedicure, blow-dried hair, false eyelashes, a bag of pretty underwear, a bag of racy underwear, a bag of super-racy/trashy-whore underwear and a massive long string of fake pearls from Topshop. I also have a few accessories which arrived in a plainly packaged box – I told Dan they were new ballet shoes for the girls – but I’m not sure about those. (In fact, I’m thinking the ‘vintage fur rabbit mask’ was a definite mistake.)

Every chance I’ve got, I’ve been posing in the mirror, squinting at my bum to see how big it looks and practising an alluring expression. Although I think I’ll need a glass of Prosecco beforehand to loosen up. (I’ve brought that, too.)

‘What do you think?’ Tilda bustles me into her sitting room, and I gasp. She’s moved half the furniture out and it looks like a photographer’s studio. There are big lights on stands, and a white umbrella-type thing and a single sofa in the centre of the room, plus a folding screen and a full-length mirror.

‘Amazing!’

‘Isn’t it?’ Tilda looks pleased. ‘If this goes well, I thought I might go into the business properly. It’s quite a racket, this boudoir photography.’

‘Have you ever used equipment like this before?’ I ask, curiously touching the umbrella-type thing.

‘No, but it’s all fairly obvious.’ Tilda waves an airy hand. ‘I’ve been googling. Is the house warm enough for you?’

‘It’s sweltering!’ I’ve never known Tilda’s house so hot. Usually she’s of the ‘heating is for wimps’ mentality.

‘You want to be nice and warm and relaxed. Nice eyelashes, by the way,’ adds Tilda admiringly. ‘And what have you brought?’ She reaches into one of my bags and pulls out the string of pearls. ‘Ah, very good. A boudoir classic. The “draping shot”, as we boudoir photographers call it.’

She sounds so expert, I want to laugh. I’m also quite touched she’s taking it so seriously.

‘You can change behind the screen,’ Tilda continues, opening up the Prosecco and pouring it out. ‘And then we’ll go into the first pose.’ She hands me a glass and consults a handwritten list headed Sylvie – Poses. ‘Sit on the sofa, then gradually slide off. Your head should be thrust upwards, right leg bent, left leg relaxed, back arched, shoe dangling …’

‘Uhuh,’ I say doubtfully. ‘Can you show me?’

‘Show you?’ Tilda looks aghast. ‘Well, I can try, but I’m not very supple.’

She sits on the sofa, then slides off. Halfway towards the floor she freezes, one leg pinned to the floor, the other swinging akimbo, and her head thrust back in a painful-looking rictus. She looks like she’s giving birth. That can’t be right.

‘Ow.’ She flops to the floor. ‘You see?’

‘Er … kind of,’ I say, after a pause.

‘It’ll be fine!’ she says breezily. ‘I’ll direct you. Now, what are you going to wear?’

Choosing the first outfit is a lot of fun, and takes us nearly half an hour. I went a bit overboard with the underwear shopping so we have lots of choice and eventually get it down to a white lace set with white seamed stockings and suspenders. As I emerge from behind the screen, I feel genuinely sexy and excited. Dan won’t believe his eyes!

‘Amazing!’ says Tilda, who is fiddling with her light counter. ‘Now, if you get into position …’

I sit on the sofa, slide down and freeze in the same way that Tilda did. Almost at once, my thighs start burning. I should have done the boudoir workout.

‘Ready?’ I say, after what seems like ten minutes.

‘Sorry,’ says Tilda, glancing up. ‘Oh, you look gorgeous. Lovely!’

She takes a few pictures, peering at me between shots.

‘Really? Are you sure?’

I want to say, ‘Do I look like I’m giving birth?’ only that might sound weird.

‘Try putting your hands behind your head,’ suggests Tilda, snapping away. ‘Oh, yes! Now sweep your hair back. Lovely! Do it again!’

Twenty hair-sweeps later my legs can’t take it any more and I collapse on to the floor.

‘Great!’ says Tilda. ‘Shall we have a look?’

‘Yes!’ I scrabble to my feet and hurry over to the camera. Tilda scrolls back through the shots and we both gaze in silence.

The images are so far from what I imagined that I’m speechless. You can barely see my face. You can barely see the sexy underwear. The whole photo is dominated by my legs in their white stockings, which are lit up so brightly, they look like luminous surgical stockings. In half the photos, my hair is over my face, not in a sexy way, but a dishevelled, crap-looking way. And I do look like I’m giving birth.

‘My legs look quite …’ I say at last.

I don’t want to say ‘huge, fat and white’. But that’s the truth.

‘I didn’t quite get the lighting right,’ says Tilda after another long pause. Her ebullience has dimmed and there’s a crinkle in her brow. ‘Not exactly right. Never mind. Let’s go on to the second pose.’

I put on a new outfit – red lace teddy – and get on to all fours, following Tilda’s directions.

‘Now, lean forward on your knees … legs apart … further apart …’

‘They won’t go any further apart,’ I gasp. ‘I’m not a bloody gymnast!’

‘OK, now raise your chin,’ instructs Tilda, ignoring me. ‘Put your weight all on one arm if you can … boost your boobs with the other arm … give me a sexy look …’

My knees are killing me. My arm is killing me. And now I have to produce a sexy look? I flutter my eyelashes and the camera flashes a few times. ‘Hmm,’ says Tilda, doubtfully squinting at her screen. ‘Could you lift your bum up for a better angle?’

With a huge effort, I try to arch my back and thrust my bum further into the air.

‘Hmm,’ says Tilda again. ‘No. Maybe I meant, lift up your head.’ She stares at her screen as though perplexed. ‘Can you get a bit more curve into your bum, somehow?’

‘Get more curve into my bum’? What does that even mean? My bum is my bum.

‘No.’ I sit back and rub my knees. ‘Ow. I need knee pads.’ I get to my feet and rub at my legs. ‘Can I have a look?’

‘No,’ says Tilda hurriedly as I approach. ‘No, better not see these ones. I mean, they’re lovely, absolutely gorgeous, but I might just delete them …’ She jabs quickly at her camera, then looks up with a bright smile. ‘That pose wasn’t quite working. But I’ve got another idea. We’ll use the doorway.’

The doorway is the worst of all. This time I insist on seeing the shots, and I look like a gorilla. A pale, hairless gorilla in a blonde wig, hanging from a door frame in a black bra and knickers. This time, all the light pools harshly on my stomach. You can’t see my face but you can see my stretch marks in glorious detail. If Dan saw this photo, we’d probably never have sex again.

‘I can absolutely Photoshop these,’ Tilda keeps saying as we scroll through, but I can tell she’s slightly losing confidence. ‘It’s harder than I thought,’ she says at last, heaving a sigh. ‘I mean, taking the photos is easy enough, it’s making them look good.’ She gazes at a particularly ghoulish image of me, winces and pours more Prosecco into our glasses.

We both take a few gulps, and Tilda idly experiments with my black satin corset, wrapping it around herself this way and that.

‘Maybe we need something simpler,’ she says at last. ‘We’ll use the failsafe pose.’

‘What’s the failsafe pose?’

‘It’s for all shapes and sizes,’ she says, more confidently. ‘I read about it on a website. You lie on the sofa, legs crossed and gaze up at the camera. I’ve got lighting instructions, too.’

Lying on the sofa sounds a lot better than kneeling on the floor, or hanging upside down off the back of a chair, which was her other idea.

‘OK,’ I nod. ‘What shall I wear?’

But Tilda is still preoccupied with my corset. ‘How does this thing work?’ she says suddenly. ‘I can’t work it out at all. Where’s the top? Where’s the boobs bit?’

‘It doesn’t have a boobs bit,’ I tell her. ‘It’s an underbust corset. You can wear a bra with it. Or not.’

‘Oh, I see. Well, perfect!’ Her imagination seems seized. ‘Wear this and a pair of knickers and nothing more. Lie on the sofa. Play with your pearls. It’ll look great. Dan will go wild.’

‘Right.’ I hesitate. ‘So … a topless shot, you mean.’

‘Exactly! It’ll be gorgeous!’

I’m not too sure. Posing in underwear is one thing. But topless? In front of Tilda?