Father and son have a special bond

Doctors were surprised when they discovered both parents were ideal matches and the couple agonised over who should make the sacrifice.

Zach's mother Jacqui was also willing to donate but in the end it was Mr Williams who had the operation.

"My dad's the best in the world," said five-year-old Zach, from Clun in Shropshire.

Zach's kidneys failed to develop properly in the womb.

No suitable donor was found for him from the donors' register and his future was bleak, so the parents had themselves tested for suitability.

My dad's the best in the world Zach Williams, aged five

Mrs Williams, 32, said: "We thought at first I would be the best donor, as I was smaller, but the doctors said the size of the organ was not important."

Mr Williams, 41, said: "Our view was Zach would want his mum with him when he came round from the operation.

"She could not be there if she was also recovering in hospital, so we decided I should go for it."

Zach and his father are now back home and the youngster is looking forward to going back to school soon.