The devastating brain injury sustained by Paul Ingle demonstrates that, even with the most rapid and effective medical attention available, boxers face the risk of life-threatening injuries every time they step into the ring.

The most acute risk is that of brain damage caused by blood clots of the sort Ingle sustained when he was felled by Mbulelo Botile in the final round.

Cumulative brain injuries in which the brain tissue is "scarred" by repeated blows are also common over a long career. These can lead to the condition known as being "punch drunk", a symptom of which is slurring of speech.

Blood clots occur when blood vessels that supply the brain are ruptured. The brain is not fixed immobile inside the skull, but is surrounded by a series of linings to which it is attached by blood vessels.

When a boxer's head is punched the skull is subject to a rapid "rotation acceleration/deceleration", the strange jerking motion in which the head rocks rapidly back and then forth.

If the force of the blow is sufficient, the blood vessels tear and clotting ensues. There are also blood vessels deeper within the brain that can be ruptured.

"The brain is like a blancmange inside a biscuit tin which works well until you drop the biscuit tin from the top of a 20 storey building, which is the equivalent of a blow from a professional boxer," said Dr Bill O'Neill, a British Medical Association expert on boxing.

The British Boxing Board of Control points out that other sports, including three-day eventing and motor racing are, per capita, more likely to lead to death.

The difference, says the BMA, is that inflicting harm is the aim of boxing. "Brain damage is an unarguable side-effect of a knockout. Acute brain damage is the most effective means of winning a fight," said Dr O'Neill.

The crucial stage in treating a brain injury is the first hour. Ingle was in surgery within 45 minutes.

Failure to react fast can be crippling. In 1991, Michael Watson suffered a subdural haemorrhage in a fight with Chris Eubank. It was almost two hours before he had a brain scan, longer before surgery.

Nine years on, Watson knows he will never use his left side, or speak smoothly or walk without extreme effort.