When Anna Campbell told her father of her plan to join Kurdish forces fighting Isis, he made a joke that he will forever regret. It was May last year, and the 26-year-old had travelled from her home in Bristol to his, in Lewes, East Sussex, to break the news.

“By then, I knew enough to know that it would imperil her life,” says Dirk Campbell, 67, “but all I could think of to say was: ‘Well, Anna, it’s been nice knowing you.’ I think I was trying to be funny, but she just looked miffed. I think she wanted me to engage with it and either go, ‘Oh, how wonderful,’ or to try to argue her out of it. But I sort of just accepted it. Ten months later, she is dead.”

Anna Campbell died on 15 March when her position was struck by a Turkish missile as she and five other female soldiers helped to evacuate civilians from the besieged city of Afrin in northern Syria. She was one of eight British nationals killed fighting alongside the Kurdish People’s Protection Units (YPG) since the first foreign volunteers arrived in the autumn of 2014.

“People have called Anna a hero and a martyr,” her sister Sara says. “But what’s really difficult for the public to fathom is that she was also this big walking bundle of love: idealist, activist, dedicated bookworm, lover of insects, storyteller, creator of everlasting childhoods …”

Yet it was as a soldier that Anna died, a beaten-up AK-47 in her hand and a pair of old trainers on her feet. Having smuggled herself into Syria, after being recruited by Kurdish activists online, she had signed up with the Kurdish Women’s Protection Units (YPJ) – all-female affiliates of the YPG, a guerrilla group in which officers are elected by their troops.

Dirk Campbell: ‘I was really proud of her. She was a 26-year-old woman. I had to trust her.’ Photograph: Teri Pengilley for the Guardian

She gave her life defending Kurdish-held territory from a Turkish invasion. Some might call it someone else’s war. To Anna, her family says, it was personal.

“It was almost as if she was searching for the perfect way of expressing all the values she held closest – humanitarian, ecological, feminist and equal political representation,” says Dirk. “Those were the issues she came to dedicate her life to, and she came to the conclusion that Rojava was where she had to go.”

This Kurdish stronghold in northern Syria is in the throes of revolution. Inspired by the ideology of Abdullah Öcalan, the imprisoned leader of the outlawed Kurdistan Workers’ Party (PKK) in Turkey, and triggered by 2011’s “Arab spring”, people have organised themselves into grassroots assemblies and co-operatives, declaring their autonomy from the state and their wish for real democracy. Anti-capitalist, Marxist and feminist ideas are flourishing, including a system of co-presidentship whereby a man and a woman share power at every level.

“We were shocked when she told us she was going there,” says Dirk, a silver-haired man with a warm smile. “But we weren’t surprised.”

Anna was 11 when Dirk realised there was something different about her. “It seems a small thing, but I remember when she was at school she protected a bumblebee from being tormented by other kids,” he says. “She did it with such strength of will that they ridiculed her. But she didn’t care. She was absolutely single-minded when it came to what she believed in.”

We are sitting in the living room of Dirk’s flat, where three of Anna’s five sisters and her brother have gathered to support their dad. Sophia, at 28 the eldest sister, brings tea. A gallery of obscure musical instruments hang along the wall, all of which Dirk, a folk musician and composer who was a member of the seminal prog band Egg, can play. Books on ecology, veganism, philosophy and politics – some Kurdish – line the bookshelf.

The Campbell household was one where politics was always discussed. “Her mother Adrienne and I were once arrested for staging a sit-in in Boots after they moved the HQ to a Swiss tax haven,” Dirk chuckles.

“Most of her early interest in activism came from Adrienne,” he says. “I remember in 2011, they went to a demonstration at the Houses of Parliament to commemorate the first Suffragette protest. They stormed the Houses of Parliament in Edwardian clothes.”

But really, friends say, it was when Anna went to university in Sheffield to study English and French that those seeds of political activism began to sprout. “The coalition had just started and the government began introducing cuts and increasing fees,” recalls one friend, who prefers not to be named. “It was a big thing and there were student occupations all over the country.”

She was soon reading less of her beloved English classics in favour of books about anarchism, feminism and ecology. She became vegan and dropped out of university after her first year because, as Dirk puts it, “she was much more interested in doing what she was passionate about”.

Anna with her mother Adrienne, who died from cancer in 2012. Photograph: Family handout

That same year, 2012, Adrienne died of breast cancer four years after being diagnosed. Anna, then 21, threw herself deeper into the life she had chosen. She had started training as a plumber, but was increasingly drawn to anti-fascist, animal and human rights protests across Europe. She became an anarchist, too, and had the letters ACAB (standing for the punk-era slogan “All coppers are bastards”) tattooed on her ribcage. “She was one of the first people to go into the Jungle in Calais to protect refugees from the gendarmes,” says Dirk. “She wrote letters to prisoners. She gave blood, was a hunt saboteur, protested the Dale Farm eviction and would always rope me into playing the Highland bagpipes at prison demos.”

In 2015, she was beaten unconscious at an anti-fascist march. “She told me a woman had been dragged into the crowd by some fascists and no one was helping her,” recalls sister Rose, 24. “So Anna covered her face so they wouldn’t know she was female and ran in head first after this woman. The fascists beat her to the ground with sticks until a policeman dragged her off.”

By the summer of 2017, her attentions had turned towards the Middle East, where the war in Syria was entering a bloody new phase. The YPG/J, backed by US airstrikes, had all but flushed Isis from large swaths of Syria’s north. But, with the jihadi group now on the run, Turkey saw an opportunity to finally cleanse its borderlands of the Kurdish forces and their revolution. Ankara has long-argued that the YPG/J is linked to its own insurgent group, the Kurdistan Workers’ party (PKK). The US and EU, however, do not consider the YPG terrorists, and have supported them since 2014.

With the Kurds’ fight for existence now on two fronts, Anna’s mind was made up. She didn’t tell her friends of her plans, just her family. She made them promise not to tell a soul. “Of course, I was seriously worried,” says Dirk. “Then, the day that she flew out, the Turks bombed a YPJ position and killed 12 women. I panicked.”

Over the months, Anna stayed in regular touch, sending texts, WhatsApp voice messages and the odd call when she could. “The thing is, whenever Anna called, she gave us a false sense of security,” says Dirk. “Every time she would say: ‘Hiya, everything’s fine. I’m just growing vegetables, sitting at a lookout post. I’m not in any fighting. It’s all a bit boring, really.’ We thought she wasn’t actually in any danger, and that she was coming back in a few months.”

What he didn’t know was that she had, in fact, been deployed to Dier ez-Zor, the stage for Isis’s bitter last stand. “I think if I had known that she was facing lethal fire I would not have been able to sleep,” says Dirk. “I would have tried to get there, to be with her. After all, who’s going to fire on an unarmed white-haired old man?”

Then, on 20 January, Turkish-backed rebels attacked the Kurdish city of Afrin. “It was like nothing I’d ever seen,” another British YPJ fighter, who asked to be known only by her nom de guerre, Ruken Renas, told me from her frontline position last week. “The bombing was really heavy, especially just before the city fell. They hit the hospital; people were fleeing. It was chaos. Hundreds died.”

Anna (on right) with a fellow YPJ fighter in northern Syria. Photograph: YPJ/PA

Nevertheless, Anna was determined to help defend the revolution she had joined. She dyed her blond hair black, and begged her commanders to let her go to Afrin. Finally, they gave in. Two weeks later, she was killed.

When Dirk thinks about the afternoon when Anna told him she was going to war, emotions conflict. “I should have taken her far more seriously,” he says. “I should have got on the internet and looked up everything that was going on. I just didn’t know enough about it. All I knew was that it was a war zone. Perhaps I could have stopped her.”

He pauses for a moment. “But, at the same time, I was really proud of her. I don’t think I had any right to stop her. She was a 26-year-old woman. I had to trust her.”

Of course, there is still the issue of Anna’s body. The Campbells want it back, but with Afrin now under Turkish control, they aren’t sure where to begin. “They’re not going to be putting bodies in a morgue waiting for someone to identify them,” says Dirk. “They’ve probably collected them all up, dumped them in a truck and buried them in a mass grave, which means that if she’s going to be repatriated, it’ll depend on DNA evidence. That will take a very long time. There will be a lot of bodies to examine.”

In the meantime, he will commemorate his daughter by continuing her fight. “I would be betraying Anna’s memory if I didn’t do everything in my power to bring the Kurds’ plight to the attention of the world. Something must be done. And it needs to be done now, before anyone else’s children are killed.”