Traces found on Gary Dobson’s coat were “microscopic”, forensic scientist Edward Jarman told the Old Bailey.

A tiny bloodstain on the collar of Dobson’s jacket, measuring 0.5mm by 0.25m , was found by a cold case team, along with several dried blood flakes in its evidence bag.

Mr Jarman said: “It’s very difficult to measure fragments of blood on such a tiny scale but we’ve suggested that the total volume could be possibly less than a couple of microlitres (cubic millimetres).”

After being questioned by Mark Ellison QC, prosecuting, the forensic scientist said the team knew the stain was caused by fresh blood because of the way it was absorbed into the fabric.

After discussing the results of DNA testing he added: “The probability that it had not come from Stephen Lawrence… is probably less than one in a billion.”

Lawyers representing Dobson, 36, and David Norris, 35, claim that the forensic evidence that allowed the pair to be charged could easily have been transferred by accident in storage, handling and transportation of the evidence over the years.

But Jarman said: “The collar stain is more likely to be the result of a primary route [direct contact with the blood source] rather than more complex routes.”

Dobson and Norris both deny participating in the gang attack that killed Lawrence in Eltham, south east London in 1993.