The Other Darrin: Bradley Walsh and Dean Lennox Kelly played Doddsy and Tonka in the film; they were replaced by Steve Edge and Renton Skinner respectively for the TV series. The unmade Interim Manager would have had Walsh returning to the role, reversing this trope.
The film was originally supposed to end with Mike quitting the England job despite his eventual success, and moving to Bolivia to coach there. The producers decided they wanted a Sequel Hook however, and refilmed the ending to have Mike proclaiming "four more years!" (In the TV series we find out that he lasted just over one year, getting sacked after losing every single match in the Euro 2004 qualifying tournament)
The planned theatrical sequel, Mike Bassett: Interim Manager would have had a German coach named Jorgen Mannstein take over the England side, bringing on Mike as an assistant due to the language and cultural barriers. However, Mannstein then left to take over as Germany national coach after their existing boss was fired due to a scandal involving crystal meth — a reference to a real-life scandal involving Christoph Daum, who was set to take over as Germany national coach right about the time the first film came out, but had the job offer withdrawn after he was caught using cocaine — leaving Mike to take over as England manager for the tournament. Following the failure of a Kickstarter campaign, however, it seems likely the film will ever be made.