He says after a day on set "firing AK47s out of cars", explosions going off around him, and glass shattering everywhere, "you get home at night and you're rushing".
That's Strike Back for you. The show, based on the novels by real-life former British Special Forces operative Chris Ryan, is an unashamed chest-beating action series. It follows Stonebridge and his more gung ho partner, Sgt Damien Scott (played by Australian actor Sullivan Stapleton, Animal Kingdom), into volatile areas where they deal to everyone from terrorists and war lords to drug traffickers and sex slave traders.
While it's not a deep psychological spy thriller, like Homeland for example, it's a gritty show about humanity, and more importantly, survival.
"Stonebridge and Scott are not necessarily good or bad, they just do what they do," says Winchester. "And I think one of the things I really enjoy about it is that Scott and Stonebridge may be working for Queen and country, and the terrorists are off 'doing bad things', but when these two factions meet in the field it's just about getting out alive. It doesn't matter what's right or wrong, it's just about being able to get up the next morning. When the shit hits the fan both sides have been taught how to survive and one of them is going to make it and one of them isn't."
As the second season kicks off things have changed in the Section 20 ranks. Stonebridge is back in Britain being a dutiful husband, suffering from a bout of Post-Traumatic Stress Disorder (PTSD), and training recruits. Scott is on a mission in Kenya, but when he gets caught by Waabri, Stonebridge heads to Somali capital Mogadishu to try and get him and British attaches Patrick Burton and Rachel McMillan (played by actress Rhona Mitra, Underworld: Rise of the Lycans, Boston Legal) out.
Winchester says it's almost like a change of roles for Stonebridge and Scott, with his character the more vulnerable and hot-headed one, while Sullivan's usual macho ladies' man becomes the reasoned and reliable one.
"We had a lot of fun with the challenges of coming into a show where you think you know all about the characters and where we were going to go and then it was completely different. So it was great to be sitting across from each other and saying, 'I can't believe I'm saying that'."
In the first episode Stonebridge is torn between his devotion to his wife and loyalty to Section 20 - and he deals with it terribly by running away to save his mate in Somalia. It's this flawed character that drew Winchester to the role almost two years ago when he first read the script.
"He's not perfect. And when you get given an opportunity to play somebody in a show it's always the brokenness that the story hinges on, because that's where drama lives.
"He's this consumate professional. He wants so desperately to be a good husband and to be a father, but he can't figure it out - and he's always been able to figure things out. And he can be quite posh. But also, when stuff goes wrong and he gets pissed off, this rougher side comes out in him and that really is who he is. I like that about him."
For a brutal and often graphic series Strike Back was a popular hit last year and as a result it had a far bigger budget to play with this time round. So there are even bigger and better explosions, more shoot-outs, and it looks more refined and moodier.
Another noticeable change in the second series is that there is not as much shagging. The sex scenes - mainly featuring Scott - seemed a little random in the first series, making you wonder when soldiers on the frontline could find time for a quickie with child traffickers and war lords on the loose.
"I joked with Sulli' all the time, I'd come on set and say, 'who'd you shag today?'," laughs Winchester. "But he did mention that it was quite a bit different this year and there is less of it because Scott's character has more of a relationship with some of his relations this season. So they've really changed the show haven't they?"
What: Strike Back
Who: Actor Philip Winchester as Sgt Michael Stonebridge
Where & when: Tuesdays, 8.30pm, Soho
-TimeOut