'where are you?' luke peers at the screen. 'in a taxi?'

'we ... went out. do we need really to see this?' i make to close down the screen, but nanny sue smoothly moves it out of my reach.

'we could pop into this new mall instead of the softplay,' i can hear myself saying on screen.

'becky, i'd like you to look at your hands.' nanny sue points with a pencil. 'they're shaking. look at your fingers twitching. they began when we first saw the sign for the shopping mall, and i don't believe they stopped until you'd bought something.'

'i've just got twitchy fingers.' i give a casual little laugh. but nanny sue is shaking her head.

'i don't want to alarm you, becky ... but has it ever occurred to you that you might have an addiction to shopping?'

a sudden snort comes from luke, which i ignore.

'shopping?' i echo at last, as though i'm not even certain what the word means. 'er ... i don't think so ...'

'look at the tension in your jaw.' she gestures at the screen. 'look at the way you're tapping the seat.'

honestly. aren't people allowed to tap seats any more?

'you have an air of desperation about you,' persists nanny sue. 'to my eyes, this is a disproportionate reaction.'

'no it's not!' i realize i sound too defensive and immediately backtrack. 'look, i hadn't been shopping for a while, it's a new discount mall, i'm only human! they were giving away free gifts! they had jimmy choo at 50 per cent off! and burberry! anyone would be twitchy!'

nanny sue looks at me for a moment as though i've been speaking gibberish, then turns to luke.

'i'm starting a new series of adult programmes. we're going to be tackling all sorts of disorders, from addiction to anger-'

'wait a minute.' i cut her off in disbelief. 'you're saying you want me to go to boot camp? luke, can you believe this?'

i turn to him, waiting for him to laugh and say, 'what a ludicrous idea.' but he has an anxious frown.

'becky, i thought you said you weren't going to shop for a while. i thought we'd made an agreement.'

'i didn't shop for myself,' i say impatiently. 'i only bought a few essential clothes for minnie. and they were all on sale!'

'your life is your own concern, of course,' nanny sue is saying. 'however, my worry is that minnie may pick up your tendencies. she already has an advanced knowledge of brand names, she seems to have an unlimited amount of money to spend-'

this is the final straw.

'that is not true!' i exclaim indignantly. 'she only spends her pocket money. it's all written down in a special book, which i showed you!' i reach into my bag and produce minnie's pocket-money book. 'remember?' i thrust it at nanny sue. 'i mean, yes, she has the odd little advance, but i've explained to her she'll need to pay it back.'

nanny sue leafs through the book for a moment, then gives me an odd look.

'how much pocket money does she have?'

'fifty pence a week,' says luke. 'for now.'

nanny sue has produced a calculator from her own bag and is tapping at it.

'then according to my sums ...' she looks up calmly. 'minnie has spent her "pocket money" until the year 2103.'

'what?' i stare at her, discomfited.

'what?' luke grabs the book from her and starts flipping through. 'what the hell has she bought?'

'not that much ...'

the year 2103? can that be right? i'm trying to do frantic sums in my head as luke examines the entries in minnie's book like the gestapo.

'six dolls?' he jabs at a page. 'in one day?'

'they were a matching set,' i say defensively. 'and they've got french names! it'll help her language!'

'what's this?' he's already on another page. 'junior dolce boots?'

'she wore them the other day! those little suede ones. you said how nice she looked!'

'i didn't know they cost two hundred quid!' he erupts. 'i mean, jesus christ, becky, she's a little kid. why does she need designer boots?'

he looks really shocked. to be honest i'm a bit shocked myself. maybe i should have added up what she was spending a bit better.

'look, ok, i'll stop ...'

luke isn't even listening to me. he's turned back to nanny sue.