When Jacqui Smith heard last week that the judiciary had effectively outlawed courtroom protection for witnesses, she thought of her conversations with the mothers of Letisha Shakespeare and Charlene Ellis.

The long and convoluted trial of four men in 2005 for the murders of Letisha, 17, and Charlene, 18, outside a New Year’s Eve party in Aston, Birmingham, set the standard for the use of “special measures” to protect witnesses in gangland murder cases.

A jury returned guilty verdicts and the killers were jailed for life but the police had also gained a vital weapon with which they could begin to break down the walls of silence that had thwarted so many investigations into gangland shootings and murders.

After that case it became possible, with the permission of a trial judge, to give witnesses anonymity, to erect screens to hide their faces, to disguise their voices and to allow them to use false names.

These “special measures” have been used again and again in serious murder cases where the danger of witness intimidation is real and present.

The House of Lords ruling in the Iain Davis case last week has thrown the future of such protection into doubt and alarmed police and prosecutors. The Home Secretary said she received news of the ruling and recalled the Birmingham case. Ms Smith said: “I thought about the mums of Letisha and Charlene and remembered what they told me about the requirement for these measures in their case and how this was the way they got justice for their daughters.”

Sandra Shakespeare, Letisha’s aunt, said the law lords’ ruling had opened the way for an appeal by her niece’s killers and raised the prospect of her family’s “worst nightmare happening again”. Ms Shakespeare said: “We have just got to hope that common sense prevails and also justice prevails because, more importantly, we cannot have those murderers back on the street.”

Cases where the identity of important witnesses has been protected include that of Abdi Noor, 22, and Mo-hammed Sannoh, 19, who were jailed earlier this month for murdering Michael Dosunmu, 15, as he slept at his home in South London.

Explore Law

• Columnists

• Law Panel

• Law Reports

• Student Law

Times Recommends

• The best legal yarns this Christmas
• Legal school 'earned £1m by exploiting bar course'
• Axe may fall on 5,000 more City lawyers