A former Director of Public Prosecutions, Sir Ken Macdonald, told Today presenter Evan Davis that "complex factors are at play" after one of the killers of James Bulger was returned to custody after breaching the terms of his release.

The Justice Secretary, he said, is "in a difficult position", over the case of Jon Venables, having to balance public interest against the state's obligation to protect citizens "whatever they might have done".

He said he backed the injunction which prevents reporting of the reasons behind Venables' imprisonment "because we don't believe that we're the sort of country where people should be able to take revenge on individuals by beating them up, or worse, by killing them.

"Whatever he's done, this man's life and his security has to be protected. That's a primary duty for the state."

But Sir Ken said the government should reveal "anything which can be revealed" while protecting Venables' anonymity.

Venables, now aged 27, and Robert Thompson killed James after abducting him from a shopping centre on Merseyside in 1993. The Home Secretary, Alan Johnson, said the public had a right to know why he was returned to custody, but refused to give details.