Peter Kay's Car Share co-star Sian Gibson has said nearly all of the laughter in the forthcoming unscripted episode is "completely genuine".
Peter Kay, who recently screened the unscripted episode and the special finale to audiences in Blackpool, said: "It's absolutely wonderful hearing an audience react to what you've been working so hard on for so long.
"We'd screened both series there in previous years and it's really rewarding, plus you get to raise a bit for charity too."
The duo are set to return as car-sharing colleagues John and Kayleigh, but this time they will be seen ad-libbing the entire episode.
Kay said he wanted to try it because it is "something original", and that he "couldn't think of any other narrative comedies that have ever made a fully improvised episode".
He added: "As Sian and myself often ad-lib when filming, we thought we'd give it a go for an entire episode."
But Gibson admitted it was difficult not to burst into laughter throughout filming.
"We were always laughing, and nearly all of the laughter you see in Car Share is completely genuine," she said.
"Peter knows how to make me laugh with just a look - so he constantly makes me giggle."
She added that the pair always make each other laugh because they "find the same things funny".
Kay explained that, without a script, they "just reacted to whatever came on the radio and just went with it, good or bad."
Car Share will finally return to television after the second series of the Bafta-winning show ended on an emotional cliffhanger last year as John failed to reciprocate Kayleigh's advances.
Viewers were dismayed when he said there were no plans to pen a further series.
However, the comic later announced special episodes - a finale to reveal what happens next for the pair and the improvised episode.
Peter Kay's Car Share Unscripted will air on BBC One at 10pm on Monday May 7.