A test case being heard in the House of Lords this week will decide when the police should pay damages if they fail to protect a witness or others who are subsequently killed or harmed.

In two test cases, police forces are accused of failing to act over death threats and, lawyers say, should be liable under the laws of negligence and human rights.

The cases are being brought by the chief constables of Hertfordshire and Sussex and will establish the extent of the State’s obligations to protect individuals in the face of known threats.

Five leading human rights organisations, including Liberty and the Equality and Human Rights Commission, have “intervened” in the case to submit their own arguments.

In the first case, the law lords have been told that Giles van Colle, 25, an optometrist, had reported to Hertfordshire police several threats made against him by a technician he employed, Daniel Brougham.

Brougham was due to stand trial on theft charges and Mr van Colle was due to give evidence against him.

But the police took no action: they did not rearrest Brougham, charge him with interfering with a witness or even cancel his bail.

In November 2000 Mr van Colle was shot dead three times at close range after leaving his shop in Mill Hill, North London. Brougham was sentenced to life for murder.

The Chief Constable of Hertfordshire is appealing against a Court of Appeal decision to award £25,000 compensation to Mr Van Colle’s parents. They are cross-appealing against the halving of their damages to £25,000 at the Court of Appeal.

In the second case, the Chief Constable of Sussex is also challenging a ruling by the Court of Appeal, which refused to strike out a claim by Stephen Smith, who was seriously injured when his former partner attacked him with a claw hammer.

Mr Smith, 39, was hit by Gareth Jeffrey after reporting to police hundreds of violent threats by Jeffrey on no fewer than five occasions. Text and internet messages he received included: “U are dead” and “I am looking to kill you and no compromises.” Smith suffered serious and lasting physical and psychological injuries.

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