A new weapon to be issued to police across the country has a serious safety flaw which can cause victims to burst into flames, according to government research.

The 'taser' gun fires two small darts into a suspect, sending a severe electric shock through the body, causing temporary paralysis.

Scotland Yard is to introduce the device next year as a 'non-lethal' weapon to incapacitate aggressors. Other forces are expected to follow.

But government researchers have discovered that, if the suspect has been in contact with CS gas - a chemical irritant used to incapacitate - there is a 'serious risk' the person will catch fire when a taser is used. The flaw is particularly significant, police sources have told The Observer, because officers would normally be required to use CS gas to resolve a situation before employing a more extreme device such as a taser.

A Home Office investigation into the safety of 'less-lethal' weapons fired the taser at mannequins covered in CS gas. In two of seven tests, they caught fire. 'In both cases, the flames produced were severe and engulfed the entire top half of the mannequin,' says its report, 'Less Lethal Technologies - Initial Prioritisation and Evaluation'.

Deborah Coles, co-director of police pressure group Inquest, said: 'We are horrified they are even thinking about this. Experience has shown when they introduce a new weapon, it is only a matter of time until it seriously injures or kills someone.'

The report concludes that there is a 'serious risk of ignition if the taser is fired at a target that has flammable solvent on their clothing. This risk will extend to all flammable environments, for instance a petrol station.'

The Association of Chief Police Officers, expressing grave concern over the report, is to recommend banning the use of tasers with CS gas.

nick.walsh@observer.co.uk