Ministers are determined to rush through emergency laws to halt the collapse of criminal cases throughout England and Wales after senior judges ruled that granting witnesses anonymity could make trials unfair.

Jack Straw, the Justice Secretary, was in talks with officials last night after the halting of a trial at the Old Bailey and with an estimated 40 other murder cases at risk.

One legal source estimates that 550-600 applications have been or are being made by witnesses for anonymity in pending criminal trials. Lawyers are also set to prepare appeals in a number of cases where evidence depended on anonymous witnesses.

Last week five law lords quashed a double conviction in the case of Iain Davis, jailed for murdering two men at a New Year’s Eve party in Hackney. They said that the anonymity granted to the witnesses made the case unfair and breached the fundamental principle that an accused person had the right to know his accuser.

Mr Straw was seeking all-party backing for legislation to be rushed through both houses of Parliament before the summer recess on July 22. A Ministry of Justice source said: “He is extremely concerned about this issue. It is a matter of public confidence in the criminal justice system.”

The announcement of legislation to allow the use of anonymous witnesses could be made as soon as Prime Minister’s Questions today or in a statement to the House tomorrow.

Yesterday the Crown Prosecution Service said that it was asking prosecutors to seek an adjournment on cases using anonymous witnesses. A spokesman added: “We are still determining the precise number of live cases affected as a matter of priority.”

Yesterday the first casualty of the law lords’ ruling was a £6 million murder trial of two men accused of shooting an East London businessman, Charles Butler. The CPS said that there would be a retrial next year. Judge David Paget discharged the jury at the Old Bailey after two months of hearing evidence and near the end of the prosecution case, the culmination of a four-year inquiry into the shooting and alleged police corruption. He told an astonished jury that the case had been derailed by the law lords decision, saying: “You have heard evidence from a number of witnesses that you should not have heard.”

Four witnesses had given evidence under false names and from behind screens.

A leading defence counsel in the case, Leonard Smith, QC, said: “My understanding is that there are as many as 550-600 applications for witness anonymity across England and Wales, which is staggering. I always believed that these applications were only made in the most serious of cases. But it seems that the police have gone totally overboard in using these provisions and it’s something that will now have to be looked at very carefully. It is for Parliament, and not the courts, to obfuscate the common law.”

As well as cases being put on hold, the law lords’ ruling has opened the way to appeals, at potentially huge cost to the taxpayer.

Lawyers for two of the four men found guilty of murdering Birming-ham teenagers Charlene Ellis and Letisha Shakespeare said that they planned to appeal.

A host of other high-profile convictions in which the jury heard evidence from anonymous witnesses could now also face challenges. They include the murders of Michael Dosunmu, Magda Pniewska, Toni-Ann Byfield and Zainab Kalokoh.

Among the cases thought to be affected are some of the most high-profile gang-linked murders of recent years. But not only gangland-related cases are affected. More than 42 police officers have applied for anonymity in the forthcoming inquest into the death of Jean Charles de Menezes.

Yesterday, addressing police officers at their conference in Liverpool, Jacqui Smith, the Home Secretary, said that she shared the frustration of the police. She said that an emergency Bill to rescue the use of anonymous witnesses was “something we are looking at very urgently including, if necessary, whether we can change the law. I certainly accept, and I said some time ago, that there is a problem here that we need to solve.”

Ms Smith added: “What I am concerned about, and judges are concerned about, is that we have a system where defendants’ rights are protected but the rights of people to be able to take part in a trial are also protected.”

Giving witnesses anonymity through the use of screens, false names and voice-altering equipment has been a key weapon in convicting dangerous villains and has proved especially successful in cases of gangland violence, organised crime and terrorism.

Assistant Commissioner Bob Quick, head of New Scotland Yard’s Counter-Terrorism Command, said: “The implications for the fight against organised crime and terrorism are very serious.”

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