Scores of trials around England and Wales appeared to be risk today as the impact of a House of Lords ruling last week begins to bite.

As Jack Straw, Secretary of State for Justice, was in urgent talks with officials over whether to bring in emergency legislation, there was the prospect of criminals walking free after the law lords' ruling that granting witnesses anonymity could render a trial unfair.

Today, a £6 million murder trial was halted at the Old Bailey, the first casualty of the ruling.

Two men were on trial accused of the murder East London businessman Charles Butler.

Judge David Paget discharged the jury at the Old Bailey today after two months of hearing evidence. Four witnesses had given evidence under false names and from behind screens.

Some politicians may seize on this latest judicial ruling as another example of judges flexing their muscles - or getting too big for their wigs.

The truth is that the law lords were merely reasserting the law, not changing it. They re-stated a long-standing common law right that an accused has the right to know who his accuser is.

That right has been whittled away in recent years with claims by witnesses fearful of being threatened if they gave evidence. Only two weeks’ ago the Home Secretary vowed to extend such protections in a crackdown on gang culture and intimidation.

Malcolm Swift, QC, who defended Iain Davis, the convicted murderer who appealed to the law lords last week, says that the practice has grown in recent years and estimates that in the last 18 months, in three out of five murder cases, there have been one or more anonymous witnesses.

Ministers are under pressure to act: the law lords themselves said that if they wanted to extend the use of anonymity, they would have to legislate for it.

John Yates, the Metropolitan Police Assistant Commissioner, has already made clear his view that the ruling is a cause for “grave concern”.

There are other ways to proceed. As Mr Swift argues a rise in a gangland culture of threats and intimidation is not a justification to whittle away fundamental rights at common law. "Fundamental principles," he says "should never be sacrificed to expediency."

Instead, police witness protection schemes can be improved; witnesses, post-trial, can be given new identities and the circumstances when judges may grant anonymity can be more tightly drawn.

In the meantime, though, if trials are not to be abandoned and a mockery made of the criminal justice system, ministers need to act – emergency legislation, in the short-term, may be the only answer.

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