Hayley Williams's family in theme park safety plea

Sunday school teacher Hayley had visited Oakwood several times with family before the accident

On 15 April, 2004, Beverley Williams waved her daughter 16-year-old Hayley off ahead of a day out at a west Wales theme park. It was the last time she saw her. Hours later the teenager fell 120ft to her death after slipping out of a carriage from the top of a rollercoaster.

Since then the family has struggled to come to terms with her death, enduring years of inquests and court cases in their fight for justice. Eleven years later and the horror of that fateful day came flooding back when they learned 16 people had been injured on a ride at Alton Towers. Now, they are calling for tighter theme park regulations in the hope future accidents can be prevented.

With tears in her eyes and a softly spoken voice Beverley Williams who lives in Pontypool, Torfaen, recalls the day her daughter died.

"It was half past three. They came banging on my door and told me that there had been an accident and I needed to go to Haverfordwest [Pembrokeshire] as quickly as possible. I didn't know what had happened," she said.

"This is going to sound strange, but there's a little town before you get to the hospital called Bethlehem. We went through this little town and it was as if I knew before I got there that she wasn't going to be alive.

"I walked through the main door [of the hospital] and Hannah [her other daughter] ran up to me and said 'she's ok, don't worry' and I thought 'thank god for that'.

"Then the doctor came in and asked me to sit down and I said to him 'if you're going to tell me what I think you're going to tell me, please don't', and I can't remember much after that."

Hydro, opened in 2002, is just 34ft (10m) shorter than Canada's Niagara Falls

Hayley had been on holiday with her mother and sister Hannah, then 13, when the accident happened during a trip with friends to Oakwood Theme Park near Tenby, Pembrokeshire.

Mrs Williams did not go with them because she was unwell, but Hayley "tucked me up in bed and said 'stay there until I came back'".

Those were the last words they spoke to each other.

Hours later the St Albans RC High School pupil was airlifted to Withybush Hospital after falling from the top of the park's water ride Hydro, her family rushing to be at her side.

But the Sunday school teacher had died "instantaneously" - killed by the impact of the 120ft (36m) drop.

'Thought she was safe'

An inquest into her death in 2006 heard a safety bar designed to restrain passengers as the ride plummeted down a near-vertical chute at 50mph, had not been lowered before it started.

A mechanical engineer who gave evidence, said the safety of the ride was "unacceptable" after tests revealed he was able to get out of Hayley's seat unaided even after pulling the bar down.

But an unlawful killing verdict was ruled out by the then Pembrokeshire coroner Michael Howells, who said there was no evidence of gross negligence by anyone involved.

Alan and Beverley Williams are calling for tighter regulations at theme parks

Hayley was familiar with Hydro, having been on it several times before, and Mrs Williams said she knew her daughter "would have thought she was safe on that ride".

"You just think they [the rides] are foolproof, the ride was only 18 months old, it cost £1.8m to have it put in," she said.

"We are not talking about amusement parks - and I'm not knocking fairs - but these rides are so much more powerful and they are multimillion pound rides that you're sending you're children on.

"You're spending a lot of money to go into these parks, you want to know they are maintained."

She added: "I never thought anything would happen. Never in a million years did I think I was never going to see my child again."

Hayley was a keen singer and had wanted to pursue a stage career at London's West End

The ride was closed for a year and when it did reopen, over-the-shoulder restraints were fitted - a step up from the seat belt and lap bars in place at the time of the incident.

In 2006, the Crown Prosecution Service said no-one would face criminal charges over Hayley's death.

But two years later Oakwood Leisure, which ran the park at the time of the accident, was fined £250,000 after admitting staff had failed to ensure passengers were safely restrained on the high-speed ride.

At the time, Hayley's father Alan described the amount as "derisory", but he said no amount of money would be ever be enough.

Now, 11 years later, he and his wife say they remain concerned about the safety of rides and were devastated to learn one had crashed at Alton Towers theme park in Staffordshire, injuring 16 people.

Of those injured on the Smiler ride on 2 June, four sustained serious injuries, including 17-year-old Leah Washington who had to have a leg amputated.

Mrs Williams, 56, said: "I just turned on the news and it was there. It was like a knife that just gets dug in your heart and just gets twisted and you think you are going through it all over again."

People at Alton Towers reported hearing 'a loud crash' when the collision on the Smiler ride happened

The Smiler carriage was travelling at 20mph when it crashed

Her husband added that the family now wanted to see theme parks adhere to tougher regulations, including regular risk assessments and site inspections carried out by the Health and Safety Executive.

"They [rides] are flirting with the boundaries of technology in the speed, the inertia and G-force involved," Mr Williams said.

"If they weren't, it wouldn't be an interesting ride to go on but they have to have the technology behind it advanced enough to prevent an accident happening," he added.

"We know you can't abolish them [rides], it's an attraction for people... we just want to make them as safe as possible."

Oakwood Theme Park has changed hands since the incident. A spokesman told the BBC that although no personnel at the park now were there at the time of Hayley's death: "There is not a day goes by that we don't think back to the tragedy that happened 11 years ago."

A Health and Safety Executive spokesman said: "The Health and Safety Executive (HSE) is the regulator for fairground rides and associated equipment used on fairgrounds and theme parks in the United Kingdom.

"HSE has designated a number of trained inspectors throughout the UK to be part of the National Fairground Inspection Team (NFIT).

"In a small number of cases where small, low risk fairground rides are located in venues allocated to local authorities for enforcement purposes, for example, science parks and shopping malls, local agreements may exist where the relevant local authority takes on responsibility for fairground rides located at the venue."

More information on the regulations can be found by clicking here.

Hayley was described by her parents as 'an angel' with an 'amazing' personality