A police officer lost a Taser stun gun after leaving it on the roof of his car and driving off.

An urgent search was under way for the weapon which was lost between Lewes and Eastbourne at about 8am yesterday.

The officer realised it was missing only when he arrived at his destination and a thorough search of the route was conducted.

The police vehicle left Church Lane, Lewes, at 8am and took a back route to Eastbourne via Ringmer, the B2124 via Laughton to Golden Cross, and the A22 to Eastbourne.

Chief Superintendent Paul Pearce, head of operations for Sussex Police, said: "Obviously our priority is to recover the weapon as quickly as possible.

"The risk is that it could be picked up by a child who could easily mistake it for a toy gun.

"The less likely possibility is that it may fall into criminal hands. We need to recover this weapon as quickly as possible. The weapon is yellow and black and looks like a plastic hand gun. It should have been stored in a pouch inside a wallet in the car.

Lib Dem MP Norman Baker, who represents Lewes, said: "It's clearly rather careless that this loss has occurred but we are all human and these things do happen. However, Taser guns can be lethal and it's very important that police make all efforts to recover it before someone is hurt.

"More generally, I question whether these particular devices are safe to use at all. There is some evidence they can cause fatalities either if they are used inappropriately or against people with particular medical conditions."

Tasers work by firing two probes at a target up to 21ft away. The probes contain sharp barbs and create a circuit to send a charge of 50,000 volts through the target who instantly loses muscle control and collapses.

Sussex Police began using Tasers last year. The weapons were first introduced in the USA where there was some concern about using electrical charges on people with heart conditions.

Trials by scientists in the UK produced no lasting or long-term effects.

Conservative MP Nigel Waterson, who represents Eastbourne, admitted he once lost his mobile phone by leaving it on top of his car.

He said: "Clearly, it was a moment's inattention by the police officer.

"Nevertheless, this is a very dangerous weapon especially in the hands of someone not trained to use it properly."

Police said anyone who found the Taser at the roadside should not touch it but should dial 999 urgently and wait for the police to come and remove it.