Alpha Mum arrives on the day of the school charity version of Britain’s Got Talent, wielding four all-in-one flared Lycra jumpsuits to wear as part of our Abba routine.

“They’re bisexual,” she says, pushing us towards the headmistress’s office to change.

“Bisexual?” asks Sexy Domesticated Dad.

“I don’t want any arguments,” says Alpha Mum, as she removes her jeans. “The shop in Camden said they could be worn by men or women. It’s just a question of how high you zip up and how much chest hair you display.”

“Don’t you mean ‘unisex’?” I point out.

“This is not the moment for dissent, Agnetha,” she says in a Swedish accent. “You need to get into character.” I crouch behind the headmistress’s desk and undress, knowing that any sexual frisson between me and Sexy Domesticated Dad will be neutralised permanently when he sees me in this outfit.

“I won’t look at your chest hair if you don’t look at mine,” says Sexy Domesticated Dad.

“You’re not taking this seriously enough,” says Alpha Mum, crossly zipping up her suit.

“You need to keep things in perspective,” says Sexy Domesticated Dad, standing in his boxer shorts. “It’s just a bit of fun.”

“Remember, it’s not participation that counts, it’s winning,” says Alpha Mum.

My hopes of an extended row so that I can surreptitiously absorb Sexy Domesticated Dad’s body are dashed when Celebrity Dad removes his T-shirt to reveal a distracting amount of chest hair. He looks apologetic.

“I had it completely waxed when I was in Gladiator, and it grew back with a vengeance,” he explains. “When I played the Sheriff of Nottingham in Robin Hood, the crew called it ‘Sherwood Forest’. It is the sign of a man firing on all cylinders, if you know what I mean.”

“You look like Tom Jones,” says Alpha Mum in horror, as someone knocks on the door and tells us it’s time to go on. She tries to zip up his suit to hide the offending hair but can only manage a couple of centimetres.

As we stagger on stage, I see Husband on a Short Fuse and our three boys staring at me in horror. There’s no time to dwell on this as the music starts and we begin our well-rehearsed Waterloo routine. As we raise our hands for the first chorus, there is an agonising yell as a clump of hair is caught in Celebrity Dad’s zip.

“Has anyone got any scissors?” I shout above the music. Someone in the audience proffers a Swiss Army knife and I start to hack of clumps of chest hair with the tiny pair of scissors until Celebrity Dad is liberated.

“You’ve sabotaged it all,” shouts Alpha Mum above the noise. But, as we look over at the judges, they hold up four cards, each showing a perfect ten.

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