A medical expert who investigated the murder of Billie-Jo Jenkins told a court blood spots found on her foster father could have been breathed out as she lay dead or dying.

Former deputy headteacher Sion Jenkins, 47, allegedly battered the 13-year-old to death with an iron tent spike as she painted the patio doors at their family home.

The prosecution alleges blood spatter invisible to the eye was sprayed on his jacket and trousers during the attack on February 15, 1997.

But the defence claims air trapped in Billie-Jo's lungs may have caused the spray when Jenkins went to comfort her on the floor and pulled her shoulder.

Professor David Dennison, who has advised the Royal Navy, Ministry of Defence and Health and Safety Executive, told the jury at the Old Bailey how he carried out a series of experiments on himself.

He said: "The results of these experiments showed that with a very small volume of fresh blood in your nose you could project it as a spray of several hundred droplets to a height of a metre and a distance of about two metres.

"Only small volumes of air were necessary.

"The first conclusion I came to was if I develop pressures inside my lungs, I hold my breath or release a blocked nose, opening a mouth, that pressure is brought up to the site of the obstruction.

"These slight pressures were sufficient to break up and project a good distance, droplets, 200 to 300 or more."

Jenkins was convicted of murdering Billie-Jo at the family home in Lower Park Road, Hastings, and jailed for life at Lewes Crown Court in 1998. He is now facing a retrial ordered by the Court of Appeal.

The trial continues.