Keep Calm Pamela. This is the message on the key ring given to me last Saturday morning by my friend, the mother of my daughter’s friend of nearly 15 years.

The best friend is organising a surprise birthday party and I’m dropping my son off at hers so that we can spend some ‘bonding’ time together while my house is decorated and the food set out.

Selfridges for a Bobbi Brown teenage makeover is our destination, followed by a spot of lunch and then home where all will be organised. Marvellous I think, this is easy; it’s all working out perfectly.

After the ‘natural look’ is applied by a disinterested, unfriendly BB make-up artist – well, at least I don’t feel obliged to buy anything – we head off to find lunch on one of the back streets behind the hell that is Saturday afternoon on Oxford Street.

But before we get too far, my mobile phone rings. It’s my daughter’s friend, speaking a little too loudly.

‘Pam, we have a bit of a problem. The key doesn’t work.’

Fortunately it’s insufferably noisy in Selfridges and I am able to slope off behind a Rolex display cabinet, while my daughter stands staring blankly at the Prada handbags.

‘Just wiggle it a bit but for God’s sake don’t break the key in the lock,’ I whisper.

‘We’ve wiggled and wiggled. It doesn’t work. Could the back door be open?’

Could I have left the back door open? For once, I hope I have.

I tell the teenage foursome (two boys and two girls), who have arrived at mine to set up, to wait while I call a friend who sometimes feeds the cat; she knows the lock can be a bit tricky. Problem solved, I think, feeling pleased with myself.

The need for speed

In the nice little independent Italian café that we’ve found for lunch I surreptitiously send a text. My daughter’s look reads ‘and who is the one addicted to screens here…?’ but she is too kind to say so.

My phone flashes again. Trying not to look too obvious, my heart sinks as I read: ‘The key won’t turn. We can’t get in.’

In a quick escape to the loo, I frantically call the cat-feeding friend and the news isn’t good. Either it’s a dud or it’s the wrong key. In the ‘busyness’ (my father says I was born busy) of the morning, could I have put the wrong key under the mat? ‘More haste, less speed, Pamela, more haste, less speed’ – in my head I hear the distant echo of my mother’s voice.

Shit, shit, shit, I think. It’s now 12.45 and they still aren’t in the house. People will be arriving in less than an hour. Speed is what I need now.

‘What’s going on?’

It’s a perfectly reasonable question and my anxiety is clearly obvious. Thinking on my feet, I use my stone lithographer friend as a scapegoat.

‘You know those prints of Simon’s that I was supposed to return this morning? Well he’s having an exhibition this afternoon. I left a key under the mat for him to collect them and it doesn’t seem to work. We need to go home’.

Quite unbelievably my daughter doesn’t get into strop, even though we’re supposed to be enjoying ‘quality time’ together for a few hours. We start walking briskly up Oxford Street. She definitely doesn’t get her patience from me; it must be her Dad.

‘Hurry, we need to hurry,’ I say, breaking into a jog.

She does too, though she does say: ‘Mum, please be careful, you’re bumping into people’.

My heart is pounding.

On the tube I make small talk in an attempt to appear normal. Each tube stop feels like 30 rather than three minutes. It’s nearly 1.30. I tell her she needs to collect her brother and then go to Sainsburys to get coffee and decorations for the cake she has made for the small party she thinks is happening later in the day.

‘I am going to run ahead,’ I say.

As I’m bounding up the escalator two steps at a time, I’m desperately trying to work out who to call first – the set up crew to say I am on my way or the friend looking after my son, who must find a way to divert my daughter for at least another hour.

Outside, my mobile network takes forever to get a signal but then the first text pings in.

‘We did it. We’re in. We did it with a stick and a hanger.’

A stick and a hanger? I’m not sure whether to be relieved or furious but there isn’t time.

In the post-party analysis I also hear about a ladder and an attempted entry through the upstairs bathroom window. I do have to wonder what the cat-feeding friend makes of this decision to allow four teenagers, one of whom later tries to set off fireworks he has found in the shed, unsupervised access to my house.

Change of plan

Just beyond the communist-style tower block that’s made it into the Britain’s ugliest buildings’ list, but is now finally being dressed in glass, I do an about turn and dash back to the underground. My daughter is ambling out, looking strangely calm.

‘Good news,’ I shriek. ‘They got in.’

Blaming my scatty side, I say that in my panic I’d completely forgotten that my son’s Godmother [this bit is true] is collecting him at 2pm. My daughter looks a little puzzled, though is clearly pleased that she has escaped an afternoon with an annoying little brother.

As we’re walking towards Sainsbury she comments: ‘It’s a bit ridiculous that they couldn’t open the door? I could understand if it was a teenager but Simon is over 50.’

I agree, feeling guilty; parents aren’t supposed to lie.

In the supermarket, I think of countless things that I don’t really need to pass time. Then I do something I would never normally do: suggest we have coffee in next door M&S. Still, she doesn’t seem to smell a rat; should I be worried about her trust in me?! Here there is no mobile reception but another quick glance at my phone tells me it’s nearing 2.45. We’re meant to be home at 3pm.

As we head out the store, my phone pings. Then it pings again, and again, and again. The first message reads: ‘We’re ready for you but Mum says you didn’t turn up.’

There are about eight new messages, one of which reads that plans have changed and now we must collect my son en route from the tube. He desperately wanted to be there for the surprise and he’s kept the secret for so long that he deserves it.

I mumble something about plans having changed yet again. My daughter offers to take the shopping home while I fetch her brother. She is tired and wants to get home to rest before the party that evening.

No, no, no, I say, trying to sound calm, here I’ll take the shopping and you do the fetching.

‘I don’t want to collect him. I want to go home. I’m tired.’

Do as you are told, I say, and she storms off, the first show of anger in the four and a half hours she has spent with a mother acting like someone with a split personality disorder on speed. I hastily call the friend who has my son.

‘She’s walking down the river, hurry can you meet her on the way’.

As my daughter reaches the crossroads, I see my friend and son approaching from the other side of the tower block.

Shit, shit, shit, I think again. They are going to miss each other; I break into a jog, heading away from home. Approaching the traffic lights I begin to shriek my daughter’s name. She doesn’t turn. This doesn’t feel real. As if in slow motion, I see my friend and son waving out of the corner of my eye so I drop my handbag and the shopping, ignore the red traffic light, and make a dash across the road reaching the closest I’ve been to a sprint since leaving secondary school.

I’m shrieking like a banshee, people are stopping to stare but still my daughter doesn’t turn. I accelerate. Just as she is about to walk up the road to the house of her best friend, who is waiting with a crowd of 18 in the kitchen at mine, she finally hears me and turns. My heart is racing and I can feel the beads of sweat forming on my brow.

‘Why are you behaving like this? Why do you keep lying to me?’

She bursts into tears. For once, I’m lost for words. I’m also out of breath.