LONDON (Reuters) - A British court fined Merlin Entertainments 5 million pounds ($6.5 million) on Tuesday over a rollercoaster crash at its Alton Towers theme park in June last year that seriously injured five people.

Merlin, the world's second-biggest visitor attractions group behind Walt Disney, admitted breaching health and safety rules over the accident on "The Smiler" ride at the theme park in central England.

Two victims of the crash required leg amputations.

The fine was announced at Stafford Crown Court, central England. Merlin had pleaded guilty to the breach at an April hearing.

"We were always aware that we would end up here today facing a substantial penalty," Merlin Chief Executive Nick Varney said.

"The far greater punishment for all of us is knowing that on this occasion we let people down with devastating consequences. It is something we will never forget and it is something we are utterly determined will never be repeated," he said.

Merlin, which also runs tourist attractions such as Madame Tussauds waxworks and Legoland, has accepted full responsibility and liability for the accident and apologised.

The firm said in November its own investigation had concluded the crash was caused by human error. It found the manual override of the ride safety control system was implemented without appropriate protocols being followed.

Since the accident Alton Towers, one of Britain's biggest theme parks, has put in place improved safety measures across all its rollercoasters.

Paul Paxton, lawyer for the victims, told Sky News his clients had been shocked by the catalogue of errors.

However, he said: "(Merlin's) response initially was excellent - they admitted blame, (made) funds available for rehabilitation, and I think we take comfort from the fact that there have been well over 20 changes made to the ride and the systems."

Merlin's trade at Alton Towers has suffered since the crash, with the firm predicting a two-year period before visitor numbers recover fully.

However, shares in the firm have increased 26 percent over the last year, reflecting robust trade in other parts of the business. They were up 0.8 percent at 467 pence at 1113 GMT.

(Writing by James Davey, editing by Kate Holton and Susan Thomas)