"If Ukraine falls… we know what happens next", former Tory MP Jack Lopresti tells Trevor Phillips from Kyiv.
Less than a year ago, he was the parliamentary representative for Filton and Bradley Stoke near Bristol - now he is working with the Ukrainian military.
Mr Lopresti is a former reservist soldier, although plays down his time in Afghanistan when asked.
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But he has returned to his past way of life after leaving politics behind.
"The last time I spoke in the House of Commons, I said that the defence of the UK began in Ukraine," Mr Lopresti - who says he prefers being called Jack (short for Giacomo) - told Sunday Morning With Trevor Phillips.
"And I've been coming here for two years now, regularly helping with charities to work with defence manufacturers in my previous constituency.
"And about a year ago, I thought to myself, well, you know, politics looks difficult for us as a party at the moment, to say the least, and if I were not re-elected, then I'd come out here and do whatever I could to help. And I knew in the back of my mind that more than likely I would end up in the military, which is where I am."
This is a somewhat different path than that taken by many former politicians - who tend to revert to careers as lawyers, lobbyists or talking heads.
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Mr Lopresti says Ukrainians are not just fighting for their own survival and freedom - but that is also "our" battle, referring to the UK's support for Kyiv.
"If Ukraine falls, if we fail here, then we know [Putin] won't stop. So, you know, this is a battle for Europe.
"And if Putin succeeds, it is a green light for dictators everywhere."
The former MP goes on: "I cannot reiterate that enough really - if Ukraine falls, that we know what comes next. Estonia, Poland, Lithuania, a war with NATO. Perhaps the Chinese will look and say, actually, these guys won't fight, so we'll move on Taiwan.
"You know, this is a must win. And that's what I'm motivated by."
Since Donald Trump's election as US president last year, there has been talk about whether talks to end the war will begin.
Overnight, Mr Trump said he had spoken to Vladimir Putin on the phone - although the Russian side has not yet confirmed the conversation took place.
Volodymyr Zelenskyy has told Mr Trump "let's do a deal" - offering the US a partnership over Ukraine's stores of rare earth minerals.
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Also overnight, Russian state media claimed that the nation's armed forces had claimed control of the Orikhovo-Vasylivka settlement in Ukraine's eastern Donetsk region.
And waves of drones from both sides attacked the other.