There was a time when the name Colin Farrell was synonymous with wild antics and hard partying. So much so, he was once voted Hollywood’s top party animal by In Touch magazine.

But then the Dublin-born actor had a lot to celebrate. In a few short years, he’d gone from unsuccessfully auditioning for Boyzone and touring Ireland as part of a line-dancing troupe to sharing screen time with acting legends Tom Cruise, Bruce Willis and Al Pacino.

No wonder he was determined to enjoy himself – he was young, rich, famous and in demand.

But that was then. Fast forward seven years or so and, bar the publicity trail when promoting his latest film, you rarely catch sight or sound of Farrell.

“For a while I was out more and I was easy to find – very easy to find,” says the 34-year-old.

“Obviously now I’m in the gaff and boring, I’m not interesting to press any more. You need X-ray lenses to get at me.”

So was it a conscious decision to give up crawling the night spots?

“Not really, it was a by-product of other decisions I made,” he replies, pushing both hands through his dark hair.

You can only infer he means the birth of his two sons – the first, James, now seven, whom he had with model Kim Bordenave, and Henry, who was born in 2009. He met Henry’s mother, the actress Alicja Bachleda, on the set of Ondine but the pair are rumoured to have separated last month.

The notion of celebrity and the pitfalls of paparazzi are examined in a sub-plot in Farrell’s latest movie, a gritty gangster thriller called London Boulevard.

Farrell’s character, an ex-con called Mitchell, becomes entangled in the life of a reclusive movie star, played by Keira Knightley.

“I can empathise [with Keira’s character], sure,” says Farrell.

For Farrell, it was the writing that attracted him to his latest role. “Sometimes you read a script and before you’ve made any conscious decisions your lips are moving and you’re saying the words and you know you’re at least into it and gripped by it and that was the case with this one,” he says, sinking low in his chair.

The story begins with Mitchell’s release from Pentonville Prison “into a world he’s both at odds with and familiar with”, explains Farrell.

“He wants to make some changes in his life but keeps getting pulled back into that world of back alleys, vitriol and batons coming out.”

Mitchell’s nemesis is Gant, a ruthless old-school crime boss played with terrifying menace by Ray Winstone.

“He’s a scary fella,” says Farrell, laughing. “I mean he’s a lovely man, the most amiable dude, he really is, but he’s a strong man, so it was really fun to play with him. It was really fun to play with everyone.”

Farrell’s rise to stardom has been fast. He won plaudits for his leading role in Joel Schumacher’s film Tigerland in 2000 which led, in quick succession, to him being cast in Hart’s War with Bruce Willis, Stephen Spielberg’s Minority Report with Tom Cruise and The Recruit with Al Pacino.

Later came Michael Mann’s Miami Vice with Jamie Foxx and the Golden Globe-winning performance for the dark comedy In Bruges.

Ask him which project he’s most proud of and the answer, after a moment’s thought, is a little surprising.

“I’m really proud of Alexander,” he says in reference to the 2004 Oliver Stone box office bomb.

“That’s regardless of how the majority of people it seems felt it turned out, and even how I did in many ways.

“But it was that experience, what we all went through as a family, in six months and three different continents. That was crazy. It was such a mad time.”

The fact he’ll admit the final cut wasn’t what he expected is pretty candid for any A-lister – but Farrell’s never been one to adhere to PR spin.

“It’s so frustratingly reductive,” he says. “You live three or four months of your life having an experience with a crew of people, and then you see it condensed, withered down to an hour and a half and it’s like, ‘That doesn’t match the profundity of what I remember, how I felt’.”

As you’d expect, he’s as honest when it comes to watching his own performances on screen.

“I’m critical enough but I think it gets awful boring, really,” he says, smiling.

“I’m not my biggest fan, so there’s not much joy in it for me.”

* London Boulevard is released in cinemas on Friday, November 26