A 15-year-old schoolboy has had his leg amputated after an horrific accident while on work experience at a stoneyard.

Michael Wilkinson's right leg was crushed when he was dragged beneath the caterpillar tracks of a mechanical digger as he walked across the yard.

The Bradford teenager lay trapped for five minutes before his screams for help were heard. He was eventually released and taken by air ambulance to St James's Hospital in Leeds.

He had lost so much blood he needed six transfusions to save his life. But his leg was so badly crushed surgeons had to amputate it above the knee in a seven-hour operation.

He then had to undergo a second two-hour operation to clean up the wound. And yesterday he had further surgery to implant a machine in a bid to clean his leg to prevent further amputation.

Michael's mother, Anita Hall, 37, paid tribute to her son's courage. Anita, a former nurse, of Fenwick Drive, Woodside, said: "He has been so tremendously brave. We have been gutted by what has happened but his bravery has totally amazed me.

"I am really proud of him. He has never been sorry for himself or cried until they measured him up for a false leg."

Michael, a pupil at Wyke Manor School, had been on work placement at Russell's stone merchants in Ripley Road, West Bowling, for just over a week, when the tragedy happened. It was part of a rolling programme of work experience for older pupils in the district's schools.

Michael's stepfather, Andrew Hall, 46, said the youngster was walking back with his lunch across the yard when the digger's caterpillar tracks caught his foot and he was dragged underneath.

Mr Hall said: "He was knocked to the ground and the caterpillar wheels went over him and completely mashed his leg.

"He lost a lot of blood and was under the machine for five minutes screaming for help, but the man in the digger couldn't hear him because he was wearing protective ear muffs.

"Someone eventually heard him and managed to get the driver's attention to stop the machine and the ambulance and police were called. I used to be a policeman and I know a bit about being brave, but Michael has shown so much bravery and courage it is unbelievable. It's remarkable how he manages to stay upbeat all the time."

Mr Hall said his stepson regularly saw his dad, Graham Wilkinson, and wanted to follow in his footsteps and become a stone dresser by trade.

"That is why the school organised the work experience at the stoneyard and he was really enjoying it."

Michael's mum said he had been lucky that the air ambulance was working on the day of the accident or he would have bled to death by the time he got to hospital.

"He needed six blood transfusions when they got him to hospital.

"They knew he was going to lose his leg. I had a look at it and there was nothing left but bone. "

Anita said her son, a keen golfer and Bradford Bulls fan, had got engaged to his 15- year-old girlfriend, Sherree Charlton, on St Valentine's Day this year.

Mrs Hall said: "He is something of a romantic.

"He was frightened she would leave him after the accident. She was devastated at first but she is coping now. She has told him she loves him and there is no way she will leave him."

Anita added: "Everybody at his school is devastated too. Michael is really laid back and a happy-go-lucky character. He's very popular."

Anita has had to face her own brave battle.

She had a brain tumour removed and suffered a stroke 14 months ago but has fought back to start swimming again and taking a psychology and counselling degree at Bradford University.

She added: "Maybe he gets his bravery from me, but he is a real hero."

Michael has been suffering nightmares about his accident and his mum has been sleeping at the hospital to be with him.

She said: "He is traumatised. He can remember every single detail and he talks about it all the time.

"He says he thought he was going to die because of the amount of blood he was losing."

A health and safety investigation is underway into Michael's accident but Mrs Hall said she is not asking questions about how it happened now.

She said: "All I am concerned about at the moment is Michael."

A spokeswoman for the Health and Safety Executive confirmed they were investigating an accident at Russell's stoneyard and the inquiry was likely to take some time.

Alan Oswin, headteacher at Wyke Manor School, said: "We can confirm that an accident took place on Friday, May 23 involving one of our 15-year-old pupils who was on work experience.

"The incident resulted in the student being taken to hospital with a serious leg injury.

"We were very upset to hear about the accident and we are in daily contact with the family and offering whatever support we can.

"The Health and Safety Executive has now launched a full investigation and we cannot comment further at this stage."

Mark Reid, a director at Russell's stone merchants, said it would be inappropriate to comment at this stage.