In 2007 I arrived in Moscow with my wife and young family. I was a career foreign correspondent working for the British newspaper The Guardian. My previous postings were to Delhi and Berlin. I had chronicled George Bush's wars in Iraq and Afghanistan, reported from the frontline and dodged incoming mortar fire. Surely Russia would be easy? Not quite, it turned out.

Within a few months we found ourselves in a badly written spy novel. Unpromising young men followed me around the icy streets. Secret agents broke into our apartment, on one occasion opening the window next to our six-year-old son's bed. We lived on the tenth floor. The UK embassy explained that these ghostly visitors worked for the FSB. This was the main successor agency to the KGB. Its former boss was Vladimir Putin, Russia's president.

I wrote about these experiences in a 2011 memoir, Mafia State (published in the US as Expelled). They fuelled much of my subsequent work as a non-fiction writer. Why had Putin's undercover agents picked on me? I was never entirely sure. My attempts to unravel the 2006 murder of Alexander Litvinenko may have played a part and certainly contributed to the Kremlin's decision to deport me from Russia, in the first case of its kind since the Cold War.

In London, I followed a public inquiry into Litvinenko's teapot assassination. It concluded Putin "probably" approved the operation using radioactive polonium. My book about the case, A Very Expensive Poison, is a dramatic account of one of this century's most lurid crimes. The playwright Lucy Prebble adapted it into an award-winning stage play at the Old Vic theatre in London; it was shortlisted for the 2017 Crime Writers' Association Non-fiction Dagger Prize.

My next book sought to answer a question which haunts us still: what does Vladimir Putin have on the former US president Donald Trump? The dossier by the former MI6 officer Christopher Steele says Putin's spies secretly filmed Trump in a Moscow hotel room. The claim always struck me as plausible; the FSB specialises in covert recordings and once left a sex manual by our marital bed. "Collusion: Secret Meetings, Dirty Money and How Russia helped Trump Win" was a number one New York Times best-seller.

Like its predecessors, my 2018 book Shadow State is a real-life thriller. The story is incredible but true. Two Russian colonels arrive in Salisbury on a mission to murder a renegade colleague, Sergei Skripal. Shadow State further describes the myriad ways in which the Kremlin is seeking to subvert our democracy and overwhelm our politics, via cyber-hacking, disinformation, and corruption.

My latest book "Invasion: Russia's Bloody War and Ukraine's Fight for Survival", is published in November 2022 by Vintage and Guardian Faber. It is the first account of a war that has transformed international relations and which has led to an outpouring of support for Ukraine in the US, UK and beyond. Invasion is a gripping and compelling first draft of history, I hope, of a story that concerns and touches us all.

When Putin's overweening assault began at 4am on February 24, 2022 I was in Kyiv. His goal? To topple president Volodymyr Zelenskiy and to wipe Ukraine from the map. As Putin saw it Ukraine was "historical Russia". I spent the early hours of the invasion sheltering in an underground car park. A mother arrived with her children; the kids' were clutching colouring books. War had arrived. It was Europe's biggest since 1945. Civilians would be its main victims. I spent 2022 on the frontline.

My focus as a writer and correspondent is on the human story. "Invasion" describes the horrors of Bucha and Mariupol; the grinding artillery battle in eastern Ukraine; and the mass graves and torture chambers found in former zones of Russian occupation. I travelled to the north-east Kharkiv region, to areas liberated in autumn by a Ukrainian counter-offensive. In November 2022 I visited bombed villages in Kherson oblast, in the south, days after a Russian pull-out across the Dnipro river.

I have also written books on Edward Snowden, Julian Assange and the Conservative politician Jonathan Aitken. The director Oliver Stone made The Snowden Files into a biopic, Snowden; Dreamworks adapted my book WikiLeaks - written with David Leigh - into The Fifth Estate, starring Benedict Cumberbatch.