But the harsh reality of life in hiding leaps off the page. Anne’s frustration at having to share a tiny bedroom with Fritz, a man she despised; using a bucket as a toilet and the monotony of eating nothing but rotten boiled lettuce for days; hiding in terror as the building was burgled. All with no privacy and no escape.

The expression of Anne’s claustrophobia is painful to read. “I wander from room to room, climb up and down the stairs and feel like a songbird whose wings have been ripped off and who keeps hurling itself against the bars of its dark cage. ‘Let me out, where there’s fresh air and laughter!’ a voice within me cries,” she wrote on 29 October 1943.

You can feel her ache to be free says Gillian Walnes, executive director of the Anne Frank Trust UK. “Here was a teenager full of life who must stay absolutely silent, her whole day lived in whispers, having to stifle every laugh. Each morning waking up to think this could be her last. In constant fear and tension.”

For Lee, too, some of the most evocative entries are those expressing Anne’s desire to be free. “She writes about being in the attic looking out at the chestnut tree, trying to sniff fresh air through a tiny crack in the window. Anne has an incredible ability to put us in those moments, we read them and will her to fly free.”

But, says Moggach, what makes the diary so wonderful is Anne’s balance of the serious and the everyday. “You can’t sit in that annex for two years and just think about the fact that you might die. Your lavatory is blocked and you’re getting your first period, quarrelling with your mother and making up again, being normal.”

So the old Anne – the precocious girl who, as her cousin Buddy Elias told Lee, “would come into a room and it would be 40 quickfire questions” – was still there, driving the adults a little nuts. The boy-crazy Anne hasn’t gone either, she falls in and then out of love with Peter, who Walnes calls, “the object of her attention, affection and growing sexual awareness”.

A normal girl

Anne’s struggles for independence and identity, alienation from her sister, frustration with her mother and wonder at her burgeoning sexuality are so universal, you can’t help but see your own teenage struggles on the page. That’s because Anne wasn’t just an extraordinary writer says Lee, she was also an incredible editor.

On 28 March 1944 she heard Dutch Cabinet Minister Bolkestein on the radio asking people to keep documents as a record for future generations. Anne was determined hers would play its part, creating an edited version of her diary. “What’s so remarkable is that when she went back over her diary with a goal of publication, she didn’t edit out the incredibly personal sections,” says Lee. “She knew they were interesting and would speak to people.”

A gimlet-eyed analysis of the failings of her parents’ marriage, the fumbles with Peter and her then-provocatively liberal view of sex outside marriage – “It’s not wrong for a man to bring a little experience to a marriage. After all, it has nothing to do with the marriage itself, does it?” – was just the start.

The entries on her changing body were some of the most controversial. “Until I was eleven or twelve, I didn’t realise there was a second set of labia on the inside, since you couldn’t see them,” she wrote on 24 March 1944. “What’s even funnier is that I thought urine came out of the clitoris. I asked Mother once what that little bump was, and she said she didn’t know. She can really play dumb when she wants to!”

These passages illustrate Anne’s skill as a writer. She instinctively knew that brutally frank and funny worked for a reader, creating a precursor to today’s confessional journalism and blogging. Lee suggests it is Anne’s searing honesty that connects with readers. “There are passages where you feel sorry for the others because of the way she wrote about them. But the person she was always most unsparing with was herself.”

The final, moving entry shows the intense internal struggle 15-year-old Anne is having: “My lighter, more superficial side will always steal a march on the deeper side and therefore always win. You can’t imagine how often I’ve tried to push away this Anne, which is only half of what is known as Anne – to beat her down, hide her.”

“She’s grappling with the two sides of personality,” says Walnes. “The precocious, flippant, sarcastic Anne, and the real Anne, wanting to take responsibility, go out and change the world. She’s fighting to let the good Anne win.” She never had the chance.

We’ll never know who betrayed them, but we do know that when the Gestapo burst in on 4 August 1944, they were incredibly close to being saved. Instead, all eight were sent to Westerbork transit camp. One girl who saw Anne there told Lee she expressed a relief to be out in the open after being inside so long. “They also thought they had a very good chance of survival. They knew the Allies were on their way.”

The life and legacy of Anne Frank