A crash on an £18 million rollercoaster which left at 16 people injured yesterday led to the closure of the Alton Towers and sent shares in its parent group Merlin Entertainments falling on the FTSE.

Two men, aged 18 and 27, and two women, aged 19 and 17, suffered "significant lower limb injuries" and were airlifted to trauma centres in Stoke and Coventry for treatment.

The Smiler, which holds the Guinness World Record for most loops in a rollercoaster, has experienced problems since it opened in May 2013. These include incidents in  July 2013 after a piece fell off the track, and 48 people had to be rescued and in November 2013 when it closed for five days after wheels fell off and hit four people in the front carriage.

Merlin Entertainments said there would be a "full investigation" and the Health and Safety Executive were already on site.