In 2009, 503 films were released in the UK. Only 4% of which were Suspense/Thriller films.
Action, animation and comedy movies count for 52% of the UK box office. This is due to a wide range of audience. Thrillers however are more selective with age restrictions, this narrows down an extremely large amount of audience. Gender also plays a bit role, because according to statistics, women are more likely to watch a thriller movie.