The government is to rush through new laws to allow witnesses to give evidence anonymously in some serious court cases, following a ruling by law lords that effectively halted the practice.

Jack Straw, the justice secretary, said the rights of defendants to know who was testifying against them had to be balanced against the risk that intimidation could put witnesses off giving evidence. He said a change to the law would be made “as quickly as possible”.

“It is fundamental defendants should be able literally to see and hear the evidence before them,” Straw told Radio 4.

“But you have to balance that against what actually happens in real life these days where you’ve got very serious gun and drug crime and there is such a high level of fear.”

Straw’s comments came after the House of Lords last week quashed the murder conviction of a man whose prosecution relied on anonymous evidence.

Lord Bingham, the senior law lord, said that the anonymity of key witnesses in the trial of Iain Davis — convicted of shooting two men dead in Hackney, east London, in 2002 — “hampered the conduct of the defence in a manner and to an extent which was unlawful and rendered the trial unfair”.

Police have warned that dozens of killers and other serious criminals could use the ruling as a precedent to appeal if they were convicted on the evidence of anonymous witnesses.

John Yates, assistant commissioner of the Metropolitan Police, said: “This is potentially disastrous. It almost feels like we have broken our word. To see clearly guilty people walking free is just awful.”

Times Recommends

• Milk: do we need a dairy godmother?
• DIY: the women doing it for themselves
• First double portrait of Princes unveiled