A nine-year-old boy will donate bone marrow to his younger sister in the hope it will cure her of a rare disorder.

Jack and Ella Elderfield will undergo the transplant on Friday at Great Ormond Street Hospital.

Their father Ross said the procedure has an 80% chance of curing his daughter of Glanzmann’s thrombasthenia, a condition that means her blood does not clot and a small cut could haemorrhage for days.

The six-year-old has had two blood transfusions, one when she was three and one in 2011, which may have been needed because of food scratching her throat.

Doctors at the Kent Haemophilia Centre, Canterbury, first mentioned the possibility of the transplant 18 months ago.

Mr Elderfield said doctors look at siblings as potential candidates for a transplant first as they stand the best chance of their marrow not being rejected.

Jack is a perfect match.

The 34-year-old, who is a youth coach at Sheerness East Football Club, said: “He had to go up and have some blood tests and he had to go to a psychiatrist to see if he was happy for him to be the donor and what his understanding of it was, which we’ve spoken to him about, and he understands what he’s doing.

“I think Ella is proud of him. He has been protective of her and she knows it's going to give her a better chance of being cured.

“The family are very pleased and he seems like a little hero, so he’s going to get a lot of praise.”

“Well, any brother could do it, but I’m quite brave” - Jack Elderfield

Speaking before the operation Jack said: “I’m not scared or anything. I’m going to have the anaesthetics and I’m going to go to sleep and they are going to take part of my bone marrow, which is like a liquid, while I’m sleeping.

“It’s going to cure, probably, Ella’s blood and that means she will be able to do things.

"She’ll be really happy. She’ll be able to do lots of things like eat sharp things, she won’t have to eat soft things.”

He added: “Well, any brother could do it, but I’m quite brave.”

Jack attends Halfway Houses with his sister and their mother Lisa Elderfield, 36, is a teacher at the school.

Ella will spend six to eight weeks at Great Ormond Street Hospital and may be off school until the new year after which she will undergo regular blood tests.