In 2014, on the eve of the Scottish independence referendum, a young BAE graduate called Paul Sweeney introduced Gordon Brown. He was there because of a referendum that “sent you into a black hole and spat you back out”, as he puts it. In his case, this started with a letter warning of the impact of independence on the shipbuilding industry, which led to a photoshoot, an appearance on the 6 o’clock news, and eventually the warm-up act for a former Prime Minister.

“Glasgow did feel like the ground was moving under your feet,” Sweeney says. “It was exhilarating, terrifying.” But unlike Sweeney, most young Glaswegians were swept up in the independence movement, and the north east of the city where he lived was one of the strongest areas for Yes.

Brown’s speech was widely acclaimed for saving the union. But in Glasgow, voters were disappointed, and in the general election, Labour campaigners “were really told where to go”. Glasgow North East, a traditional Labour seat, fell to the Scottish National Party.

And yet, just two years and a snap election later, Sweeney is sitting in Westminster’s Portcullis House, as the constituency’s new Labour MP. How?

“From a very young age, I sensed an area that had fallen from a previous glory”

Sweeney, a fresh-faced 28, was ambitious for his constituency from a young age. “I was brought up in a Labour family – a working class family – in the north of Glasgow,” he tells me. “From a very young age, I sensed an area that had fallen from a previous glory.”

His mother, who worked in the Bank of Scotland, grew up in Milton, a housing scheme in northern Glasgow. “My mum used to talk about how it was a lovely area and lots of families there.” But by the time he was a child, drug abuse was on the increase, and “despair crept in”. Visiting his grandmother had to be done on foot: “You couldn’t drive a car in there because it would be vandalised.”

Sweeney’s father was a shipbuilder. In the 1990s, as shipyards fell silent, he was made redundant several times. “I remember getting up to see him off going to Barrow-in-Furness [in Cumbria],” Sweeney says. “I remember not getting much for Christmas because money was tight.” His father eventually became a taxi driver.

Sweeney, though, increasingly felt compelled to fight the decline. He studied politics and economics at Glasgow University and enrolled in the Territorial Army, before graduating and joining the defence giant BAE. In 2015, he moved to Scotland’s economic development agency, Scottish Enterprise.

At the same time, he joined Labour, inspired by the late John Smith, whom his parents called “the greatest leader my country never had”. In 2009, he was doing his exams, when Sarah Brown, wife to then-prime minister Gordon Brown, called and asked him if he wanted to help Labour’s candidate Willie Bain in the Glasgow North East by-election.

Sweeney joined a team that included Kezia Dugdale, the future Scottish Labour leader. The Tory candidate was one Ruth Davidson. He recently reminisced with Dugdale about the by-election: “We were saying who would have thought all these changes would have happened in a relatively short period of time.

The Yes badges were the cool thing to have – now it was Jeremy

Bain won, but was swept from office by the SNP’s Anne McLaughlin in 2015 in such an upset that Sweeney started his 2017 campaign only hoping to reduce her 9,222 majority. With little funding, he relied on a team of young volunteers to design leaflets and door-knock.

Then something changed. Was it the Corbyn surge? “Absolutely – without a shadow of a doubt,” he replies.

Initially sceptical of Jeremy Corbyn, Sweeney believes his “vision of hope” revived Labour’s fortunes. In Dennistoun, a hipster neighbourhood known for its SNP and Green vote, all the posters in the windows were Labour ones. “It was sexy again,” he says. “The Yes badges were the cool thing to have on your school bag. Now it was Jeremy.”

One day, a group of young men began shouting at the canvassing team. “We thought, ‘Here we go,’ then it actually turned out they were shouting ‘C’mon the Jez, let’s get Jeremy in.’ It was people who you wouldn’t normally think would vote. I thought that was fantastic.”

All the same, Sweeney didn’t bother drafting a victory speech. He describes the count as “like you are flying through the air”. When he knew he had won, his first thought was: “Oh, shit, I need to do an acceptance speech."

One of my best friends was killed in Afghanistan

Now safely landed in Westminster, Sweeney hopes to draw on his experience in industry and the military. The latter has taught him caution, not jingoism.

“One of my best friends was killed in Afghanistan,” he says. “It was a terrible time. It was just unbelievable. He went there because he wanted an experience. He wasn’t in the army as such – he was captain of the Scottish Lacrosse team.

“It does lead you to ask, ‘What are we doing? What is the meaning behind this? The intent is noble but there is a certain amount of ignorance about what needs to be done to achieve the political outcome.”

Afghanistan’s troubled Helmand Province, he points out, is the size of Wales: “We are trying to control it with 8,000 people.”

On Trident, an issue that traditionally divides Labour’s pacifists from its hawks, Sweeney’s view is also nuanced. “Trident actually saps services from other ship building industries,” he says. “There was a huge investment on the Clyde and money has to be diverted now. It is robbing Peter to pay Paul.”

Sweeney calls himself “restless” for change. He hates “energy vampires”, as he calls those that stand in the way. But while the spectre of economic neglect has clearly driven his career, he is also excited about ideas of nationalisation and regeneration.

“My family are steeped in the Clyde ship building,” he says. “Sitting on your dad’s shoulders watching these ships being launched – it is an extraordinary achievement.

“You can understand why it was so emotional when the ship building declined. It was part of their identity. These are the largest objects made by man. It is incredible to behold.”