He's since been described as the next big thing in Britain, and is to appear in two more big-budget British dramas this year: Testament of Youth (with Kit Harington) and Legend (with Tom Hardy).
"It's all a bit of a mind-job, but I'm not complaining," he says with typically self-effacing British charm.
His co-star Sophie Cookson, who plays Roxy, is equally bemused by all the new attention.
"I never thought I'd be in an action-blockbuster, full stop, let alone so quickly out of drama school. I still can't really believe it now. It's all very bizarre."
The pair play two youngsters who are invited to join an ultra-competitive and top-secret training programme, from which one survivor will be recruited to the mysterious Kingsman service - an off-the-radar independent intelligence spy organisation that bases its codes of practice on being a gentleman. The service is headed by none other than Michael Caine (codenamed Arthur), and Colin Firth takes on his first action blockbuster role as Agent Harry Heart (codenamed Galahad). Mark Strong plays the tech-wizard and trainer of new recruits (codenamed Merlin), and Samuel L. Jackson plays the mad criminal mastermind.
That's quite a line-up of top-class actors to work with as a newbie, and the way casting worked out meant the old-school experienced spies teaching the fresh recruits in the film was echoed in the real world too, with veteran actors giving a hand to foster new talent.
Sophie Cookson didn't think she would ever be in an action blockbuster.
"All the actors who play the recruits had never done a film before, which I think scared the bejesus out of Matthew [Vaughn] but for us it was brilliant," Cookson explains. "It works in the favour of the film, the audience don't have any preconceptions about where these young characters are going to go, and it was a nice mix of people."
"It also meant that we were cheap," Egerton says with a grin.
Roxy comes from a traditional upper-class private school background, but Eggsy is an unrefined but talented street kid whose father was a Kingsman, killed when Eggsy was very young while saving the life of Harry Heart. Heart feels indebted to Eggsy, and when he gets into a spot of bother with the law, Heart gets him released to find out whether Eggsy has similar talents to his father.
Eggsy never had dreams of being a spy or a hero, but it turns out he's quite good at it anyway, and finds it a real thrill. Egerton found his own experience to be somewhat similar.
"I was quite a sensitive boy really, I was playing with toy animals and things in front of the television, so this was a bit of a stretch for me, but I enjoyed it immensely. We don't quite have the same comic book culture as America, but I would watch Spiderman cartoons, and X-Men cartoons, and watch Bond as much as anyone on the planet. It's quite a thrill to be playing a hero."
Both of them had to learn a number of new physical skills for the roles - shooting, skydiving, fighting, surviving a near drowning, wielding an umbrella as a weapon. The new skills didn't come easy to the active 20-somethings, though.
"It was a lot of hard work," Egerton says with a grimace.
Cookson adds: "I've always liked sports, and doing physical things, but there's a difference between enjoying that in your personal life, and having to do it on demand over and over for a film.
"There's a mental strength required I think. Just doing that stuff so many times, like doing the underwater scene over and over for two weeks, when it was supposed to be done in four days. Getting in and out of the water, constantly freezing cold because it was the middle of December, getting into dry clothes, and then jumping in and doing it again."
Kingsman walks that fine line of paying homage to, and taking the mickey out of, the great legacy of spy films, so Egerton and Cookson were conscious of looking to the past for points of reference. But both also found their characters to be different from anyone that's gone before.
"Eggsy isn't really a recognisable type from the spy genre," says Egerton. "Towards the end he begins to more closely resemble someone from that genre, and I guess subconsciously there was probably a bit of Roger Moore in there, that thing of doing it all with a raised eyebrow. That's the persona he's adopting anyway, he doesn't like to take things too seriously."
"For me, there aren't actually that many filmic female references for Roxy," Cookson adds, "so I read a lot. I read about women who were working as spies in the time of Churchill and the second world war, and I read Charlotte Gray and William Boyd, they were my references really."
Cookson found personal parallels in Roxy having to overcome the challenge of being the only female recruit. "Filming is still predominantly quite a male environment, and I was definitely often the only girl on set, so I can definitely relate to Roxy in that way."
However, Egerton found Eggsy's personal struggles to overcome his background and class stigma less relatable to his own circumstances.
"I'm not from an affluent background, but I think Eggsy has had a really tough time, whereas I've always been very lucky to have a supportive family, and I'm from a very nurturing background.
"I would have to have some tragedy and romance in my life," he jokes, "but I've actually had a very cushioned, caring, upbringing. I'm desperately seeking some edge. Maybe I'll find it one day."
Some would say he's already found that edge by becoming Britain's newest rising male star.
Watch the trailer for Kingsman: The Secret Service below:
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Who: Taron Egerton and Sophie Cookson, rising British film stars
What: Kingsman: The Secret Service
Where and when: In cinemas from today
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