My gut feeling about sequels is that they should be premeditated: You should try to write a trilogy first or at least sketch out a trilogy if you have any faith in your film.
I loved the material when I first read it and the experience of making the film was a great one. So when we came around to complete the trilogy I just signed on board without even reading the scripts because the experience of the first film was so good.
In the 'Garnethill' trilogy people always forget that Maureen O'Donnell's dad was a journalist and she did art history at uni and her brother did law but no-one ever thinks they're middle-class - they're just working class because they speak with accents.