The notoriously rainy English climate has wreaked havoc on the schedule of more than one film production. But it was also the inclement weather that gave rise to Simon Pegg’s new comedy adventure Paul.

‘During the rain-soaked shooting of his first film, Shaun of the Dead, producer Nira Park asked him what he was planning for his next project.

Fed up with rain delays, Pegg joked: ‘Let’s make a film somewhere it never rains, like a desert.”’

‘That day, over lunch, Simon handed me this drawing of an alien with a tagline that read, “In America, everyone’s an alien,”’ remembers Park.

‘He said, “This is our next movie – a road trip with an alien.”

We talked about it a bit and how the film would be shot in the American South West. After that, I pinned the piece of paper on my drawing board and kept thinking about it.I thought, ‘What a brilliant idea.’”

‘At the end of Hot Fuzz, I reminded Simon again about the idea.I said, “Why don’t you just write up the first scene…just to see?” Simon returned ten minutes later with a scene, and it was just fantastic.’

Park sent the copy to Eric Fellner at Working Title Films, who snapped up the idea. After she heard back from Fellner, Park phoned Pegg.

She said: ‘I told him, “He wants to do it!” and Simon said, “Who wants to do what?” and I said, “That thing!” By the time we started filming, we realised it had been six years since he gave me that piece of paper.

I had it scanned and gave it to the director, Greg Mottola, on the first day of filming.’

Paul marks the first screenplay Pegg and his frequent co-star Nick Frost have written as partners.

‘Nick and I have worked together for ten years and we’ve been friends for much longer,’ Pegg says: ‘The collaboration has been an interesting experience, because we’ve slightly changed the dynamic of our characters in this one.

In the other movies, which I wrote with Edgar Wright, I played the main character and Nick is the sidekick. But this film is very much a doubleheader. If anything, Nick’s character, Clive, is slightly more dominant and confident.’

Before putting pen to paper, Pegg and Frost set out on a factfindng road trip in an RV across the American West, from Los Angeles to Denver... where they encountered terrible weather, including heavy snow and temperatures so low that their camper van’s battery froze.

It was the same problem when they eventually returned to the region for the actual filming.

‘We wound up shooting in one of the most changeable places in the world,’ Pegg says. ‘It would be blazing sunshine one minute and 20 minutes later there’d be hailstones the size of golf balls.

Sometimes we had to take cover due to lightning storms.

‘There was even a device on set to ensure we were a safe distance away from electrical storms, because apparently a lot of people get struck by lightning in New Mexico.’

Nonetheless, Pegg said that they ‘learned so much about the landscape’ from their fact-finding trip, adding: ‘It was extraordinarily beautiful, hospitable and inhospitable at the same time, remarkable country.’

They wove several of their experiences from the trip into the script.

‘We actually went to a place called the Little A’Le’Inn, and the incident in the film with the meatheads happened to us,’ recalls Pegg. ‘There were these two guys who came in who were perhaps not quite as threatening as the characters in the movie, but they certainly made the atmosphere turn cold. The bird hitting the windshield also happened.

Every day there was a new experience. We had a real adventure. It was vital and brilliant fun, and we never could have written the movie without it.’

Since they couldn’t take an actual extraterrestrial on the trip with them, the duo came up with a suitable substitute.

One of Pegg’s friends sculpted a bust of an alien and called him Paul.

‘All the photos they sent were framed in such a way that Paul looked like he was with them,’ says producer Park. ‘That brought it to life. They suddenly thought, “You know, this could really work.” ‘

Once the excursion was over, Pegg and Frost watched more than 50 movies about aliens and about road trips.

‘Then we just sat opposite one another and banged it out, line by line,’ recalls Frost.

‘For a time Simon went off to do How to Lose Friends & Alienate People, and since we needed a draft of the script, I went away for a couple of weeks and wrote a big 180-page script.

When Simon returned, we took that behemoth and completely deconstructed it. We kept what was good, and what was bad was elbowed. Simon had a big monitor so I could see what he was typing. We discussed every single line, sometimes for hours.’

As Pegg sees it, Paul’s cast is a ‘coming together of the comedy communities in the US and the UK’.

Pegg and Frost represent the British contingent, and the other principal members of the cast are notable American comic names, many of whom have previously worked with director Greg Mottola.

Though his physical presence would ultimately be the work of the CGI wizards, Paul was voiced by Seth Rogen, who altered the character’s personality. ‘At first, Paul was much older and grumpier, much more of a curmudgeon than he is now,’ he says.