Criminal practitioners have urged the government to consult properly before ploughing ahead with emergency legislation to allow witness anonymity, which they fear could jeopardise fair trials.

Ian Kelcey, chairman of the Law Society’s criminal law committee, said: ‘The home secretary should stop and think about the dangers before forging ahead with potentially far-reaching legislation that could lead into the abyss of injustice.’

The Criminal Evidence (Witness Anonymity) Bill, being debated in Parliament this week, was introduced following the House of Lords ruling that English law did not permit evidence to be given anonymously.

Kelcey accepted that in a small number of cases witness anonymity may be necessary, subject to appropriate safeguards, but said it should be limited to the most serious cases.

‘There’s a real worry that once these powers become law, they’ll be used too frequently and become the norm rather than the exception,’ he said.

Sally O’Neill, chairwoman of the Criminal Bar Association, said the measures were already too easily offered by police officers to get witnesses on board.

Rodney Warren, director of the Criminal Law Solicitors Association, said: ‘Everyone wants to ensure justice is done and that includes appropriate and adequate protection of witnesses. But it’s also a fundamental aspect of justice that a defendant knows their accuser.’

Lord Chancellor Jack Straw said allowing witnesses to give evidence anonymously had played a vital role in convicting the most violent criminals. A Ministry of Justice spokeswoman said there will be further opportunity to consult as the bill goes through Parliament.