COLIN FIRTH is still hoping he might have got away with it. He constantly reassures himself that most people leave the cinema as soon as the credits begin to roll and only those few who meandered towards the exit doors will know of his embarrassment. Why? Because when Mamma Mia! hit cinema screens in July to rave reviews suddenly people weren’t so eager to beat the traffic out of the car park.

Word had got out that there was something worth waiting for at the end of the film.

So when Meryl Streep finished singing her final number, looked at the camera and asked the audience if they wanted more, they stayed where they were and watched with anticipation.

And on came Colin Firth, Pierce Brosnan and Stellan Skarsgard dressed head to toe in outlandish Spandex suits to sing Waterloo.

Reputations that had been fostered over entire careers were swept aside in an instant. To borrow a line from the song, they couldn’t escape if they wanted to.

“That wasn’t part of the deal at all,” says Colin, still cringing at the memory. “We’d finished filming in Greece, they were wrapping things up, and there was a debate going on about whether we were going to shoot that final number at all.

“And then they decided they would and produced those suits. It was very late in the day so we couldn’t back out.”

Of course, everybody got the joke. The actors played up to the camera and the audience left the cinema with an even bigger spring in their step from the summer’s ultimate feelgood movie.

For Colin, who admits his singing skills are negligible, a sense of humour was vital throughout. 

“No matter what actors tell you about what motivates them or how they want to change the world, what we really want is to put on a frock and mince about with mascara on,” he jokes. “So Mamma Mia! was a dream come true.

“It just seemed like such a silly idea, it was irresistible. It felt like a party was being thrown in town and I didn’t want to miss it. I couldn’t make head nor tail of the script, I didn’t know what it was about. You try reading a script that is largely made out of Abba lyrics!

“So I had to go and see the show to find out what it was about and, even having seen the film as well, I’m still a bit confused! 

“But it’s incredibly good fun, there’s a kind of exuberance to it you don’t find in a lot of films. I think it’s very hard to achieve that and it’s fantastic to be a part of it when it’s happening. 

“Watching the main characters, the ones who can really sing, at the top of their game, was fantastic. I’m very glad that we don’t live in a world of cultural films alone. It’s brilliant that there are films like Mamma Mia! and that they work sometimes.

“People asked how we came together as a family — blind terror is very bonding! I showed up on the first day of pre-record terrified of meeting Benny and Bjorn — I’d heard they were hard task masters and they’d booked three days to record a three-minute song.

“My mind boggled as to how we would fill those days, imagining myself in floods of tears while they shook their heads and ordered me to do another take.

“And then I was introduced to Pierce and I was staring into a vortex of terror, and it was the same with Stellan and I realised I wasn’t alone in this. Within half an hour, we were like The Andrews Sisters around the microphone!”

After letting his hair down to such an extent, fans of the romantic heart-throb who first wooed BBC viewers as the brooding Mr Darcy in Pride and Prejudice will be reassured to know that Colin’s next work sets about restoring that reputation.

In Then She Found Me the actor plays a newly divorced father-of-two who begins a complicated relationship with his young son’s teacher. 

Tortured and disillusioned by his break-up, Frank (Firth) struggles to let down his emotional guard and allow anyone else in. His trust takes a further battering when his fledgling romance with the also recently separated teacher is hit by her discovery that she is pregnant by her now estranged husband.

The film also stars Helen Hunt (As Good As It Gets) and Bette Midler.

“It would be dull to play someone whose life is easy,” smiles Colin. “I can’t think of an interesting film about someone who’s having an easy time of it. 

“Drama is always about conflict. Life isn’t easy for Hamlet or Romeo. If it looks easy on the page then it’s not properly written. They’ve got to have some obstacles.”

The youthful looking star (it’s hard to believe he will be 48 on Wednesday), follows that up with another challenging role in Genova, a film by Michael Winterbottom in which he plays a widowed father-of-two who moves with his daughters to Italy to start a new life.

“I made Genova at the same time I was making Mamma Mia!, which was quite a contrast,” he says with a degree of understatement.

“In fact the whole of 2007 was one of the most bizarre experiences of contrast that I’ve ever known. I’d been working on a documentary with my wife about a death row case in America, a lot of which was to do with racial tension. It covered the nature of political dissent in the States, certainly amongst African Americans, and how that has changed. You don’t really get the same sort of rhetoric that you used to get from Martin Luther King and Angela Davis — most of it seems to come through things like rap music now. So we interviewed Snoop Dogg for the film.

“I remember one week in particular where I started it working on the St Trinian’s movie kissing Rupert Everett in drag and finished it interviewing Snoop Dogg in Amsterdam.

“Then I went on to the set of Genova, which is about a death in the family and a father raising his girls, and then back into Spandex and Lycra for an Abba number. It was a bewildering contrast.”

Not that he’d have it any other way. 

Born in Hampshire, the young Colin spent much of his youth abroad. Both his parents were born in India and his father, David, worked as an education officer for the Nigerian government where Colin lived for four years. He also spent a year in St Louis, Missouri when he was 11.

Little wonder that his first movie role was a film called Another Country. 

“I do find that life and art have a habit of imitating each other,” says Colin. “I have a son who grew up in the States and in Canada (from a relationship with actress Meg Tilly) and I’ve spent a lot of my adult life in North America. 

“Now I find myself playing the Englishman in America role quite a lot.

“I met an Italian woman and learnt Italian so that I could be a more convincing life partner (Colin married Italian film producer/director Livia Giuggioli in 1997), certainly where her family was concerned, and nobody knew that and then they wrote that part for me in Love Actually where something very similar happens.

“I don’t know what draws these things together but sometimes it’s quite striking.” 
It sounds like something Abba would sing about, in fact.

Then She Found Me is released at cinemas on September 19.