The noise and the energy in the streets is extraordinary. Porchey and Major Phillips struggle to keep their little party together. Even Crawfie is letting her hair down and singing along with everyone else. ‘We’ve got the blues on the run,’ she joins in with Elizabeth, laughing, while David Bowes-Lyon keeps a firm hold on an exhilarated Margaret’s belt.

‘We should try and stick together,’ Porchey shouts in Elizabeth’s ear.

He’s worried, she can see. Normally she would do her best to stop him worrying. Normally she would be sensible and agree to go back. She knows Porchey can’t relax and enjoy himself as he deserves to. It’s not fair on him. She should suggest they all return to the palace.

But she doesn’t want to.

This is her one chance to be ordinary, to be invisible. It will end, of course it will, but surely she can be allowed a little longer?

‘Let’s dance,’ she shouts back, tipping the sailor’s hat to a rakish angle. ‘We’ll stick together that way.’

People are climbing up lamp posts and onto the dignified lions in Trafalgar Square, splashing into fountains and pulling each other up onto cars as makeshift stages to dance and kiss. Elizabeth watches one couple who have made it onto the plinth of a statue exchange a lascivious kiss, their hands roaming frantically over each other, and her eyes widen.

Porchey follows her gaze. ‘Oh I say,’ he says as he pulls her away. ‘We’d better leave them to it.’

Elizabeth nods, but as they romp onwards she can’t stop thinking about that uninhibited embrace. It’s like an itch behind her eyelids. What would it be like to be kissed like that? Her blood booms at the thought, and she thinks about Philip, still so far away.

The movement of the crowd is taking them back towards the palace. Elizabeth would like to go the other way, but the people around her have other ideas. Whooping and cheering, they surge back down the Mall, bearing Elizabeth, Margaret and the others with them.

‘We want the King! We want the King!’ the crowd shouts, and Elizabeth links arms with her sister as they look up at the palace. It is a view she has never seen before. The balcony looks so small, so far away. It is empty now, but inside her parents will be exchanging glances and getting to their feet. Her mother will be putting on her hat and gloves, making sure her lipstick is in place.

‘Isn’t this amazing?’ Margaret yells into Elizabeth’s ear, and Elizabeth nods and squeezes her sister’s arm.

By unspoken agreement, they join in with the calls for the King and Queen to appear, and when their parents do step onto the balcony, the sisters cheer themselves hoarse.

I will never forget this night, Elizabeth thinks. She can’t wait to write and tell Philip what it has been like. She can’t wait for the war with Japan to be over.

She can’t wait for him to come home and for the future to start.