“I had heard about him before I met him,” she says, “and I was really quite surprised when this very young man arrived, looking quite shy. He certainly wasn’t what you expect a KGB man to be!”

She was meeting friends for drinks on her birthday (“I always joked afterwards that he was my birthday present,” she says) and Alexander accompanied a friend of hers who was nervous about her safety because of her involvement in a case he was investigating.

“Sasha gave you so much confidence. He supported you, he protected you, you felt very confident around him, whether you were his wife, his friend or his child. I never thought I could feel so loved, so protected and so happy.

“He was always very open-minded, open to anything new. I never thought I would find all of those qualities in one person.”

She also, of course, remembers the last time they spoke, and tears prick her eyes as she recalls leaving his hospital bedside to go home to Anatoly for the night.

“I told him: ‘Don’t worry, I’ll be back soon’,” she says. “He said: ‘I love you so much’, and he looked so sad. I tried to make a joke by saying ‘finally you tell me!’, but it was the last thing he said to me. Two hours later he was unconscious.”

Campaigning for justice can be lonely work, and Marina does not rule out marrying again one day, saying the idea of having another relationship “isn’t a problem to me”, but that any suitor would have to realise that “Sasha will always be in my life, so it would have to be a strong personality to accept that because most people want to be the only one”.

At the start of our interview, before bombarding her with questions about her husband, about Ukraine, about Putin, about Roman Abramovich and so much more, I ask her if there are any particular messages she wants to get across, and her answer comes as a surprise.

“Firstly, I’m worried about Russophobia,” she says, without pausing for thought. “Of course I support sanctions against Russia, but now people don’t even want to play Russian music, they want to boycott Russian composers. It’s stupid. The past 100 years have not been good for Russia, but it is also the country that produced Tolstoy, Dostoyevsky, Tchaikovsky and Prokofiev.”

She accepts that it might seem odd to some people that she is so passionate about defending the country that murdered her husband, but she believes that “there may be a chance for Russia to become a different country” in future.

Could she ever see herself going back to a Putin-free Russia if a modern-day Gorbachev were to take over one day and bring about a new glasnost?

“When I left Russia I didn’t think I had left forever,” she says, recalling the couple’s arrival in the UK as political refugees in 2000. “There were people who left during the Cold War that knew they were leaving for good, but for me I thought it was going to be temporary.

“Now, though, I would be more happy to go to live in Ukraine. It’s a very similar culture; I have friends there and there will be plenty of work to do in rebuilding the country once the war is over.”

She praises British people for being so “welcoming and open” to taking in Ukrainian refugees, but warns that “they need to be serious about it. 

“It’s not just about being generous; it’s about being capable of supporting people who are traumatised, who have just come from a war zone. People also need to be prepared to be in this for the long haul; you can’t just reject someone after a couple of weeks.”

She does not have space in the small flat she shares with her son to be able to house a refugee, but is acting as a liaison for others who want to open their homes. She admits the war took her by surprise – a few days before the invasion, Moscow-born Marina was in Ukraine visiting friends in the south-west of the country.

“I didn’t think there was going to be an invasion at all,” she admits, “or certainly nothing beyond the Donbas region. There were so many reasons for Putin not to do it, especially the effect that sanctions would have, that I thought he would hold back.”

She says the West has been guilty of a collective failure to see Putin for what he is – “someone who has turned Russia into a mafia state and then a terrorist state” – because successive leaders have convinced themselves they knew how to handle him.

“During the Cold War it was simple, because the West didn’t really have any personal relationships with Russia,” she says. “But after glasnost the West started doing business with Russia, private companies got deeply involved, personal relationships formed and they wanted to give Putin the benefit of the doubt.”

She recalled George W Bush’s meeting with Putin in June 2001, when the US president said he had “looked the man in the eye” and found him to be “straightforward and trustworthy… I was able to get a sense of his soul”.