Police chiefs in Thames Valley are planning to extend trials of high-voltage Taser stun guns following a year's trial.

The Taser stun gun

A 12-month pilot scheme in five police forces ended at the weekend, but the Home Office has not yet made a final decision on whether the guns should be used nationwide.

The weapons, which incapacitate suspects with a 50,000-volt electric shock, have still not been fired in earnest by Thames Valley Police officers.

In the first six months of the year, they were deployed 23 times in Oxfordshire at armed response incidents but never used.

Kate Smith, a spokesman for Thames Valley Police, said: "We do plan to extend the Taser gun trial but the Government is now deciding how long the extension should be for and what shape this will take. "To date, there have been no Tasers discharged in the force area but they have been deployed on numerous occasions and were found to be very effective in bringing a dangerous situation to a safe conclusion.

"Tasers have been shown to work as a good deterrent in conflict situations."

But Amnesty International argues that the guns have not been properly tested. It says several people in the US and Canada have died after being shot with the stun guns.

It has called for full medical trials to be carried out before the Government allows the stun guns to be issued across the country.

Taser guns fire needle-tipped barbs up to 26ft to deliver a disabling, 50,000-volt shock. They are considered a less lethal alternative to conventional firearms.

But some officers have expressed concerns about the stun gun's reliability. In three cases more than one discharge was required to subdue a suspect, and on other occasions the Taser did not seem to fire correctly.

But the stun gun was thought to have significant "deterrent effects".