Human rights campaigners and Britain's largest police force have expressed doubts over plans to make 10,000 Taser stun guns available to officers across England and Wales.

Home Secretary Jacqui Smith today announced that £8m would be made available to increase the supply of Tasers and to train 30,000 officers to use them.

But Amnesty International claims the 50,000-volt guns have been responsible for 320 deaths in the US, and the Metropolitan Police Authority said their use by non-specialist officers could damage public confidence.

Smith's decision follows year-long trials of Tasers by frontline officers in 10 police forces. The guns, only deployed in the UK by specialist firearms officers, deliver a powerful electric shock that temporarily incapacitates targets and causes them to "freeze" or fall to the ground.

Oliver Sprague, an arms expert at Amnesty International UK, said: "We don't oppose the use of Tasers as long as it's by a limited number of highly-trained specialist officers, responding to genuinely life-threatening or very dangerous situations.

"Tasers are potentially lethal weapons, which are already linked to numerous deaths in North America, and that's why wide deployment without adequate training is a dangerous step in British policing."

He said the human rights group's research showed that 320 people had died after being Tasered in the US since 2001, and that 90% of those killed were shocked multiple times and were not armed.

A Metropolitan Police Authority spokesman said: "The MPA recognises the potential to cause fear and damage public confidence if the use of Tasers is extended to non-specialist trained police officers and is perceived by the public to be indiscriminate.

"There is no doubt that in some circumstances Tasers are a very effective alternative to firearms or asps [metal batons] but their use must be tightly controlled and we have seen no case made out to extend their availability."

The home office minister Alan Campbell told BBC Radio 4's Today programme that during the trials Tasers had been deployed more than 600 times, but used on only 93 occasions.

According to the BBC, police officers in England and Wales have fired the stun guns more than 1,000 times since 2004. The Independent Police Complaints Commission said 35 complaints about their use had been received since 2004.

In 2007, a Polish man, Robert Dziekanski, died after being Tasered at Vancouver airport in a notorious incident that was captured on video.