I think in most couples or partnerships, there's a constant struggle for power and dominance.

The film [Sightseers] is really the story of the journey of a relationship, so the killings are almost a metaphor for the trials they go through. We wanted people to identify with the experience of going on holiday and having a quarrel with your wife, boyfriend, whatever. We knew if we didn't crack that it would not be watchable as a film.

'Sightseers' started off as a character comedy double act.

We developed 'Sightseers' as a TV idea but didn't get anywhere with it because all the channels said it was too dark originally as an idea for television.

I think it's very easy to get discouraged early on.

We always wanted to make a comedy that was a little bit more than that, which had tragic elements to it... that people engaged with - an intelligent comedy essentially.

I think what's difficult is proving to people that a script actually does work and sometimes the laughter might not be on the page, it might be between the lines.