Ricky Gervais is never short of a word or two (and acerbic ones at that), but it would seem he's finally met his match. Keeley Bolger catches up with the comedian and his caustic co-star, Constantine the frog.

When Ricky Gervais mentions his era-defining hit The Office, the usual response is for people to listen in captivated awe.

Today, his audience is a little harder to please. In fact, a mere mention is met with a deafening snore. "Sorry, sometimes I fall asleep when he starts talking about himself a lot, which is all the time," explains Constantine, Gervais' minuscule co-star (he could be Kermit the Frog's doppelganger; a dark mole above his mouth being the only thing that distinguishes the two) who plays the 'World's Number One Criminal' in new movie Muppets Most Wanted.

Perhaps Constantine, who speaks with a thick Russian accent, has heard of Extras, another of Gervais' TV hits?

"Is that like when you need a newspaper? Extra, extra?" asks the Muppet, who's dressed in a T-shirt that reads 'I'm Not Kermit'.

This blase approach to Gervais' career may be unusual given the comedian and writer's numerous Bafta wins, Golden Globe presenting slots and Hollywood hits, but it's clear from the regular peals of high-pitched laughter that erupt from the 52-year-old Brit that he's having a blast next to his felt friend.

A lifelong Muppets fan, Gervais, who used to watch the popular puppetry series in the Seventies with his older siblings, was thrilled to land the role as the "lead human" in the new film, which sees the entire Muppets gang, including Kermit and Miss Piggy, heading to Europe for a much touted tour.

"I've been a fan of the Muppets for many years, but this is my first time acting opposite a frog. It's probably the best experience of my life. This is a big Hollywood production. The sets are amazing, the effects are great, it's a really funny caper plot," explains the star, who recently announced that he has plans to film a mockumentary series following his Office character David Brent as he tours with his band, Foregone Conclusion.

There is plenty of adventure for the Muppets, as they go overseas and find themselves unwittingly entangled in an international crime caper headed by baddie Constantine and his dastardly sidekick Dominic Badguy ("Badgeee, it's French"), played by Gervais, who also acts as the Muppets' tour manager.

The Derek creator and actor isn't the only human making an appearance in the movie. There's also Modern Family actor Ty Burrell, who plays French officer Jean Pierre Napoleon, Tina Fey as Nadya, a Russian prison guard who has a soft spot for Kermit, and a constant stream of cameos, from Gervais' Office co-star Mackenzie Crook to Salma Hayek, Chloe Grace Moretz, Tom Hiddleston, Stanley Tucci and Miranda Richardson.

Fans of The Office might recall Gervais' limb-flinging, wince-inducing dance in an episode of the early Noughties series, but the idea of dusting off his dancing shoes again for Muppets Most Wanted wasn't a welcome one.

"[I found the dancing] a bit awkward," explains Gervais, who also sings in the film (he was actually in a pop duo, Seona Dancing, during his final year of university). "I'm not a great dancer but he's [Constantine's] a great dancer. His little flippers can go nine to the dozen."

"19 to the dozen," corrects his puppet friend.

Gervais, who worked in events at the University of London Union before attracting the attention of television executives, has worked with classic children's characters before. But unlike his experience with Constantine, it's unlikely that Elmo gave him any lip when the Reading-born star strummed him a lullaby on Sesame Street, back in 2009.

And Gervais probably didn't attract any flack from the furry favourites when he had a very small part in the last Muppets blockbuster, The Muppets, in 2011.

The scene was eventually cut, with the director James Bobin explaining, "It wasn't right for the movie", but the film-maker knew that Gervais would be a "fantastic" fit for his next movie.

"There were loads of cammies [cameos] in the last film. I filmed it in about an hour the day before I did The [Golden] Globes so I wasn't a big part at all," reveals Gervais, who's also the author of a bestselling children's book called Flanimals.

Constantine, who calls Gervais "a great big Number Two", is keen to know more. "When James [Bobin] call up and say, 'Listen mate, that scene has been cut', was your feeling hurt?" he enquires in his broken English.

"I said, 'Don't worry about it'," replies Gervais, laughing.

"Like, 'I don't care, you don't pay me anyway?'" continues Constantine.

"But this time do you know what he is?" adds the frog, leaning forwards. "He is big star of the movie. He up on poster, his name is on poster."

Gervais collapses into another round of the titters.

"Sometimes these things [interviews] are a bit awkward," he says, catching his breath. "They're not much fun, but with an evil Russian frog, everything's all right."

Evidently his time with the Muppets scores well on Gervais' career highlights.

"The Office was good, Extras was good, Golden Globes was good," he notes.

"But [as for the best part of my job] this is it, talking to an evil Russian frog in a little T-shirt."

Extra time - Famous faces in Muppets most wanted

:: Lady Gaga - The pint-sized pop star makes a blink-and-you'll-miss-it appearance in the first singing number, where she pours a cup of tea and trills about celebrity cameos alongside crooner Tony Bennett.

:: Ray Liotta - The Goodfellas star plays prisoner Big Papa who is banged up in a Siberian gulag (labour camp) with other celebrity cellmates Josh Groban and Jemaine Clement.

:: James McAvoy - The Scottish actor pops up as a delivery man who presents Sam The Eagle, an all-American Muppet, with a giant police badge.

:: Celine Dion - As fairy godmothers go, Celine Dion proves to be a pretty entertaining one for Miss Piggy, giving her the full benefit of her golden lungs in a rousing singalong. Although, as Miss Piggy says: "With a little help from moi, I think Celine may have a big future in singing."

:: Hugh Bonneville - Towards the end of the comedy caper, the Downton Abbey patriarch pops up as a disgruntled journalist.

:: Muppets Most Wanted is released in cinemas on Friday, March 28