Following the incident at Alton Towers, which saw a carriage full of people crash into an empty one on the Smiler, four rollercoasters operated by Merlin Entertainments at parks across the UK have been closed until further notice.

The Smiler incident left four people with “significant lower limb injuries”, one confirmed as a double leg break, after the two carriages on the ride collided earlier this week.

When Alton Towers reopens “within the next few days” the Smiler will remain shut, as will Thorpe Park’s Saw rollercoaster and Chessington World of Adventures’ Dragon’s Fury and Rattlesnake rides. Ride manufacturer Gerstlauer designed both Saw and the Smiler, while Maurer Söhne developed Dragon’s Fury and Rattlesnake.

"Since the accident at Alton Towers Resort on Tuesday afternoon Merlin Entertainments has been engaged in a thorough review and investigation of the events that led up to the incident and of its safety and operating processes. The investigation is ongoing and we are co-operating fully with the Health & Safety Executive," said a statement from Merlin, which owns and operates all three theme parks

"The safety of our visitors is our fundamental priority. We have a strong safety record at Alton Towers and across the Merlin Group. Today we are enhancing our safety standards by issuing an additional set of safety protocols and procedures that will reinforce the safe operation of our multi-car rollercoasters. These are effective immediately.

"Each rollercoaster has its own individual operating process and characteristics. Our central safety management team, together with local park operations, will now work to implement and brief operating staff on these protocols. As a consequence, two rollercoaster rides have been withdrawn from service until the new safety protocols have been applied.

"The Smiler and Saw, a similar ride at Thorpe Park, have been closed since the accident and will stay closed for the foreseeable future. We intend to complete our thorough appraisal of our safety processes at Alton Towers in the near future and plan to re-open the Park to the public in the next few days."

“This has been a terrible experience for everyone involved and one we sincerely regret," added Merlin CEO Nick Varney. "Our thoughts remain with those who were seriously injured and we are doing everything we can to support them through this difficult time. It is an accident that should not have happened, and we are determined that it will never happen again."