Alton Towers operator Merlin is due in court today for a verdict on the Smiler rollercoaster crash which left two people needing leg amputations and several others with serious injuries.

The operator is expecting to be hit with a heavy fine – expected to be in the millions of pounds – after pleading guilty in April to breaching health and safety laws.

A total of 16 people were injured in June last year when their carriage collided with an empty one.

Representatives for the Health and Safety Executive (HSE) have said that the Gerstlauer-manufactured £18m (€16m, £13.9m) Smiler, which opened in 2013, never had a "proper settled system" for staff to follow if a carriage stopped on the track.

An investigation into the crash revealed in November that the accident was the result of human error when a worker at the park had manually overridden the ride safety system. The investigation did not find any technical or mechanical problems with the ride itself.

The Smiler reopened in March for the first time since the accident. During its closure, the ride was equipped with new safety features, including technical improvements. Staff were also given additional training and the park has also added further protocols to the manual override process so that a senior staff member has to authorise and action the decision. Additional surveillance cameras and additional staff inspection checks have also been put in place.