New warnings have been sounded over the supposedly non-lethal Tasers being introduced to UK police forces after hundreds of deaths were reported in the US.
A new report claims greater use of Tasers in America and other countries has seen vulnerable people suffer disproportionately.
Amnesty International, which compiled today's report, said 334 people had been killed in the United States after being shot by Taser since 2001.
The Liberal Democrats warned the weapon could signal a slide into US-style policing.
"It is vital that we have an in-depth inquiry from the home affairs select committee into the use of Tasers before they are commonplace on British streets," said Lib Dem MP Tom Brake.
"There are serious concerns that giving Tasers to more officers is taking us on the slippery slope to fully-armed, US-style policing."
Amnesty looked at the results of 98 autopsies and discovered 90 per cent involved victims who were unarmed and did not pose a serious threat.
The Home Office, responding to direct calls from Amnesty International, said Tasers would only be given to specially-trained officers facing serious threats of violence.
According to Amnesty International's arms programme director Oliver Sprague, some incidents have seen people exposed to repeated or prolonged shocks, sometimes involving more than one officer.
Mr Sprague said that of those who died, some were shocked when they failed to comply with officers' commands after being Tasered once.
Amnesty International research has also revealed that US police forces have used Tasers on schoolchildren - including an 11-year-old girl with learning disabilities - pregnant women and an elderly person with dementia.
"As our findings from the US reveal, Tasers are potentially lethal and are inherently open to abuse. They can inflict severe pain at the push of a button, without leaving substantial marks," Mr Sprague said.
"The Taser is clearly a dangerous weapon and should only be used in very limited circumstances where strictly necessary to protect life or avoid very serious injuries. It must be kept in the hands of a small number of highly trained specialist officers."
While industry testing shows Tasers to be non-lethal, today's report claims that tests are not carried out on vulnerable people. Independent tests conducted in Canada revealed ten per cent of Taser brands to be more powerful than specified.
A source at Scotland Yard told inthenews.co.uk that raising health and safety fears over Tasers, which are "excruciatingly painful" and deliver shocks of up to 50,000 volts, was an "old familiar line".
Officially, the Metropolitan police said only "highly trained" officers - often the first on the scene of violent situations - were given Tasers and that their use was closely supervised.
Commander Bob Broadhurst said a high level of transparency was "absolutely key" in maintaining public confidence in their use.
"Every use of a Taser will continue to be monitored, with independent scrutiny from the [Metropolitan police authority]. There is a robust system of accountability including unique identification on each discharge; downloads from the Taser itself and mandatory reporting of public complaints," he said.
'Not a single death'
The Home Office told inthenews.co.uk that since Tasers were introduced in 2004 they had been deployed 3,000 times and had not contributed to a single death.
"Everyday the police put themselves in danger to protect the public and so we are committed to providing the police with the tools they tell us they need to confront dangerous people," a statement said.
"We have undertaken rigorous and unprecedented testing of Taser, submitted these devices for independent medical assessment and we are advised that the risk of death or serious injury from the use of Tasers is very low.
"We have made very clear that Tasers will only be used by officers in specially trained units who are facing serious threats of violence."
A source added that there was a "myriad of reasons" to explain the fact that zero deaths had been recorded as a result of Tasers in the UK compared to 334 in the US.
Amnesty International's Mr Sprague said that officers regularly deployed with Tasers was "one American practice we definitely do not want to see replicated here in the UK".
"We must never put dangerous electro-shock weapons like Tasers in the hands of anyone but highly trained specialist officers," he continued.
"The UK government has to commit to ensuring that Tasers are only used in life-threatening situations and that they are given to a small number of specialist officers. Otherwise the consequences could well be disastrous."
Data compiled by the Independent Police Complaints Commission, seen by inthenews.co.uk, showed a surge in Taser use earlier this year after a pilot involving ten police forces did not lead to an increase in complaints.
This led home secretary Jacqui Smith to call for even greater use of Tasers, but the plans were stung by the Metropolitan police authority saying it had no intention of sanctioning an increase in Tasers.
The Met watchdog said such a move could "cause fear and damage public confidence".