The Director of Public Prosecutions in England and Wales, David Calvert-Smith, has said retrials should be possible in "exceptional cases".

Mr Calvert-Smith was appearing before the Commons Home Affairs Select Committee to give evidence on proposals to change the so-called "double jeopardy" rule.

This is the law in England and Wales which means a suspect cannot be tried twice for the same crime if he or she has been acquitted of an offence based on the same facts.

'Stringent safeguards'

The Law Commission, which was asked by Home Secretary Jack Straw to look into the issue, recommended the law be changed in the light of the murder of Stephen Lawrence.

The change had also been proposed in the report by Sir William Macpherson into the murder.

Three of the five suspects in the Lawrence case were acquitted of the teenager's murder.

Asked whether he believed the law should be changed, Mr Calvert-Smith said: "There should be stringent safeguards, I'm a strong supporter of the law against double jeopardy but I believe it should be possible for exceptional cases to be reopened."

He warned that if a case was "stale" it would be impossible to try a defendant again, but added: "We have had examples when it has been possible to try an accused for an offence over 50 years ago, in recent war crimes cases."

Mr Calvert-Smith said he believed it should be a High Court judge to make the decision to hold a retrial.

There should also be a right of appeal, he said.