I have done a bit of hunting on a theme park tour forum they say the best time to go.

Is late september-early october.

Kiddies go back to school at the beggining of september, weather permitting is mildly warm.

Average waiting time for the popular rides are between 8-16 minutes for alton towers.

fast track says 0-6 mins.

Average body count per day mon-fri 4,897

weekend 9,567