There's an air of authenticity that can make watching The Trip uncomfortable. Essentially a fake foodie travelogue following Steve Coogan and Rob Brydon as they review a series of the world's best restaurants. They started in the north of England, series two moved to Italy and now the dining duo are heading to Spain. It looks and feels like a documentary, Coogan and Brydon playing exaggerated versions of themselves bickering, showing off and desperately trying to impress each other with their impressionistic skills (their duelling Michael Caines is a joy to behold).

The vast majority of the dialogue is improvised which makes it feel even more genuine. 'You're constantly in a state of trying to invent some fiction,' explains Brydon. 'Or a half truth, or find a truth and bend it a little bit to make it interesting. It was quite full-on.' This level of realism has led to some confusion, Brydon admitting some people believed he genuinely had an affair while filming in Italy.

It also puts added pressure on Brydon and Coogan as they are front and centre in nearly every scene. 'Generally speaking people always ask me what the food was like but to be honest that is the last thing on my mind,' says Brydon. 'I'm thinking about what I'm going to say and asking myself if I am going to be funny. If I am going to come up with anything … but usually stuff comes along. It's always nice if you make someone laugh, especially someone like Steve who I have so much respect for.'

The Trip has literary leanings. The great romantic poets featured heavily as they drove through the Lake District; their journey along the coast of Italy vaguely tracked the route of Bryon and Shelly. For the third series they follow in the footsteps of poet and novelist Laurie Lee (As I Walked Out One Midsummer Morning) and Cervantes (Don Quixote) travelling over 1000 miles through the heart of Spain. Which all links back to the first time Coogan and Brydon worked together with writer and director Michael Winterbottom on the 2005 adaptation of 'unfilmable' novel Tristram Shandy: A Cock and Bull Story, which similarly featured the pair playing themselves. 'We come in and do our thing but it's very much his baby. He's the one who decides where we're going, which restaurants we go to and the broad themes that we're going to talk about. But then we invent the majority of the dialogue, with the exception of the plot, which is needed to move the story on.'

There are moments of pathos, humour and drama but it's the aforementioned impressions that provide the funniest laugh out loud moments. 'Every time we've done The Trip I've thought ahead a bit, done some research and learned a few new voices.' Adding Andy Murray and Barry Gibb to his repertoire but there are some depths Brydon refuses to plumb. 'I've been listening recently to Donald Trump's voice and thinking to myself how it's an impressionist's dream because there are so many quirks in it. It's full of identifiable traits that are easy to copy. But I loathe the man so I can't bring myself to do him.'

The Trip to Spain premieres on Sky Atlantic and NOW TV, Thu 6 Apr, 10pm (full series on Sky Box Sets the same day).