Exclusive: Guardian investigation finds PIs have been hired as part of harassment campaigns and in some cases have tracked women to domestic violence refuges

As Laura stood in the court witness box, preparing to tell magistrates about her ex-husband’s obsessive nature, she flicked through the prosecution’s evidence file and saw the photographs. One of her leaving the house, another of her driving her car on the motorway. They had been taken by a professional. Staring at the grainy images, she felt numb.

Laura’s ex-husband had hired a private investigator to put her under surveillance. On two occasions she had been trailed, with the PI taking photographs of her as he went. Her ex-husband was later sanctioned with a stalking protection order, but the man he hired to facilitate his harassment was never even questioned.