The purpose of an sequence is to establish the mood and visual character of a film , to introduce to all or some of the following elements:
Characters:

In London to Brighton we are introduced to the mother and daughter straightaway,

Locations:

 these are two of the main settings/location of the film the train station obvioisly the main set as the mother and daughter are en route to Brighton.

Narrative/Plot

The narrative is clear from the opening sequence. It is evident that the mother has done something wrong and in doing so she looks for safety in Brighton.

Themes

Violence is a them in london to brighton. from the mothers apperence we can connote that she may have beeen in a fight. this is denoted by her black eye and graized lip.

Genre

London to Brighton is a  crime/drama Thriller genre . in this scene the thriller genre is shown at best with the daughter worried who is on the other side of the door. With the audience left in suspence the girls face further develops this.