Fifteen hundred people have been moved to safe houses in the past three years as part of a national service to protect witnesses facing intimidation, according to latest government figures.

The numbers reflect a problem that has been growing in recent years as increasing numbers of criminals resort to threats against witnesses in an attempt to escape justice. A national witness mobility service has rehoused witnesses and their families safely in about 500 cases, involving 1,500 people, since 2005.

The need for such a service is highlighted by figures suggesting that a third of vulnerable witnesses would have been unwilling to give their testimony without special measures, such as video links or screens to obscure them from the defendant, being in place.

Police in England and Wales estimate that unless the Government finds a speedy solution to the House of Lords ruling, an estimated 40 cases could either collapse or be abandoned, or defendants could have their findings of guilt quashed on appeal.

The hiding of witnesses in court has become more common in part because previous attempts at witness protection have been poorly managed. People in protection schemes have complained of being abandoned by the authorities.

Many people with vital information are reluctant to enter witness protection arrangements that could involve them being uprooted from their homes and relocated hundreds of miles from their families. Those witnesses asked, instead, that they be allowed to stay in their neighbourhoods and the police remove the menace of the gangs.

The Home Office’s action plan on gang violence, published last month, envisaged more extensive use of protective measures for witnesses. Jon Murphy, the senior policeman who drew up the plan, said that the Lords ruling revived the threat of gang violence.

“To get a case to trial requires an enormous amount of effort on behalf of the police and moral courage on the part of witnesses,” Mr Murphy said. “This decision is a massive blow to all who are struggling to remove violence and intimidating offenders from the streets.”

Ken Jones, the president of the Association of Chief Police Officers, said that the law was not fossilised and had to evolve to look at communities afflicted by gang violence. He said: “We need to look at this from the perspective of neighbourhoods plagued by insecurity and fear because of lethal gang violence.”

He added that anonymity had become a vital tool in difficult prosecutions. “Anonymity has been used in a tiny, tiny minority of cases and the fundamental principle that you are entitled to hear from your accuser has not been breached,” he said. “These powers are used only in rare and exceptional circumstances. The judiciary have supported them for a long time and there are rigorous checks and balances.”

Other countries are grappling with similar issues. The United States operates the longest-established witness protection programme.

The US scheme, operating under the 1970 Organised Crime Control Act, offers secret and permanent relocation of witnesses and their families to places of safety and, if needed, new identities. In 2000 the scheme had a budget of $24 million (£12 million) and involved more than 16,000 people.

In Italy, witnesses involved in drugs, mafia or murder offences and all crimes carrying a sentence of between five and twenty years are eligible for protection. The Central Protection Service in Italy had a budget of £72 million in 2000 for 5,000 participants.

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