Anonymity Bill 'within fortnight'

Mr Straw told MPs urgent action was vital to prevent a "significant" number of serious cases being jeopardised by a Law Lords ruling against the practice. An emergency Bill, still being drafted, will be published next week and pushed through before MPs leave Westminster for their long summer break.

"Anonymous evidence is these days fundamental to the successful prosecution of a significant number of cases, some of which involve murder, blackmail, violent disorder and terrorism," Mr Straw said. "Such cases could be jeopardised if we do not quickly fill the gap created by their Lordships' judgment."

The legislation will set out details of the process for allowing witnesses to remain anonymous and require that a judge "will have to be satisfied that the need for anonymity is satisfied, that a fair trial will be possible and that it is in the interests of justice".

Although the new law will be rushed through, it will be revisited as part of a package of legal reforms due to be introduced in the next parliamentary session, Mr Straw told MPs.

Shadow justice secretary Nick Herbert said the Opposition would try to be "constructive", but warned that the history of such emergency lawmaking was "not a happy one".

Top police officers and prosecutors have demanded the use of anonymous witnesses be enshrined in law before Parliament rises for the summer recess, warning courts could otherwise face a deluge of appeals at a potentially huge cost to the taxpayer. Police believe up to 60 people convicted of serious crimes in London alone could walk free if witnesses refused to reveal their names in a retrial.

Lawyers for two of the four men found guilty of murdering Birmingham teenagers Charlene Ellis and Letisha Shakespeare in 2003 have already said they plan to appeal. Other high-profile convictions that could face challenges are the murders of Michael Dosumnu, Magda Pniewska, Toni-Ann Byfield and Zainab Kalkoh.

Meanwhile, dozens of trials across England and Wales were effectively put on hold as prosecutors assessed the wide-ranging implications of the ruling.

Among the cases thought to be affected are some of the most high-profile gang-linked murders of recent years including the two-month Old Bailey case involving the prosecution of Douglas Johnson, 27, and David Austin, 41, for the alleged contract killing of east London businessman Charles Butler, 50. The two defendants now face a retrial next year.