A medical expert said it was impossible to believe Sion Jenkins got blood spots on his clothes from battering his foster daughter to death.

Professor Robin Schroter said the tiny particles would only have travelled 20cm in the air during the ferocious attack on 13-year-old Billie-Jo.

He told jurors at the Old Bailey: "I find it hard to believe how you would achieve the impacts if you were that close."

He said it was more likely the blood spots had been breathed out and carried on the air.

He said: "From the spot sizes I think these spots would not have got there by simply being fired through still air for the distances necessary to catch on his clothing. For exhaled particles it's a totally different scenario.

"Small particles can travel distances if that exhaled air contains small particles. They would be taken with the package of air."

Defence barrister Christopher Sallon QC asked: "If Sion Jenkins beat Billie-Jo with a tent peg, many of the spots could only have travelled a matter of centimetres if the air was still, is that correct?"

Prof Schroter replied: "If the head was beaten and spots were exhaled from it, small particles would not travel very far - the order of 20 to 30 centimetres.

"Larger particles would travel further distances. The small particles could only have got there by beating if he was within that distance. I find that impossible to believe."

The prosecution alleges former deputy head Jenkins, 47, battered his foster daughter to death with an iron tent spike.

It says blood was sprayed on his clothes in the attack at the family home in Lower Park Road, Hastings, on February 15, 1997.

Jenkins was convicted of the murder and jailed for life in 1998 but is now facing a retrial ordered by the Court of Appeal.

It is claimed he was on edge because he lied in his application for the headteacher's job at William Parker School in Hastings. Jenkins claimed he had ten grade A O-levels from Gordonstoun College in Scotland when he had only two passes and had never been to the school.

Jenkins denies murder. The trial continues.