But then he remembered how Hendrie had warned him to tell no one anything. All you need is one person you trust to let slip to someone else they trust a seemingly innocent detail and they tell another person – who they also trust – and the next thing you know you’re in a damp basement having to explain yourself to the Gestapo, which is not something any amount of training can really prepare you for.

In fact, they had tried to prepare him for such an eventuality. They’d brought up a couple of MI5 interrogators, with whom he spent an unpleasant few hours in a barn, and then a Danish army officer had come to interrogate him in Danish. He was roughed up a bit, then blindfolded and forced to stand in the dark with his hands and feet bound for what felt like hours. The consensus was that he handled these mock interrogations very well: he was unflappable, managed to think before he answered without any undue hesitation, demonstrated a degree of physical bravery and had quickly mastered his backstory – the legend, as they insisted on calling it. ‘You’re jolly good,’ Hendrie told him when the interrogation training ended, as if he was surprised. ‘However, you need to understand that unfortunately that doesn’t count for an awful lot once the Gestapo get their hands on you. The most important thing is to use this training to stop yourself falling into their hands. Don’t be cocky: they’ll smell that a mile off. That and fear.’

Greta Poulsen was spending more time in Derbyshire now, though every few days she’d return to London, where she was helping with preparing his documentation.

‘Important you feel comfortable speaking Danish,’ Hendrie told him.

‘I always have done, sir. The language came naturally to me and I always spoke it with my mother.’

‘Even so, you’ll have to speak it under pressure when you’re there. Take advantage of Miss Poulsen being around, but do be careful about how much you let on. Remember, Mr Gilbey and I are the only people who know all the details of your mission.’

The last three days at the farmhouse moved at a frantic pace. Greta returned to Derbyshire on Sunday, and she seemed to have caught the solemn mood. For two hours she sat in a room with Prince and Hendrie as they went through everything that had been prepared for him: the clothes with Danish labels, the Danish toiletries, the odds and ends and scraps of paper to go in his pockets and wallet.

‘And here’s your identity, Thomas: you’re Jesper Holm. In this envelope is your identity card – your legitimationskort – in that name along with various other documents. And here,’ she handed him a file, ‘is Jesper Holm’s story.’