British police have fired Tasers hundreds of times at suspects' chests despite explicit warnings from the weapon's manufacturer not to do so because of the dangers of causing a cardiac arrest, the Guardian can reveal.

Following the death last Wednesday of a man in Manchester after police hit him with a Taser shot, figures obtained from 18 out of 45 UK forces show that out of a total of 884 Taser discharges since 2009 – the year when Taser International first started warning the weapon's users not to aim for the chest – 57% of all shots (518) have hit the chest area.

There is evidence that shots to the chest can induce cardiac arrest. Dr Douglas Zipes, an eminent US cardiologist and emeritus professor at Indiana University, who last year published a study that explored the dangers of chest shots, told the Guardian: "My admonition [to UK police] would be avoid the chest at all costs if you can."

He said the proportion of shots landing on the chest was huge, adding: "I think the information is overwhelming to support how a Taser shot to the chest can produce cardiac arrest."

The manufacturer's warning in its training materials is clear. It states: "When possible, avoid targeting the frontal chest area near the heart to reduce the risk of potential serious injury or death.

"Serious complications could also arise in those with impaired heart function or in those with an implanted cardiac pacemaker or defibrillator."

Firing at the back is the preferred option where practical.

Zipes said Tasers were first found to have the ability to "capture" heart rhythm in a way similar to that of a pacemaker after Taser itself commissioned a study on pigs published in 2006.

If fired close enough to the heart, the 50,000 volt weapons have the ability to interfere and take over the electrical signals in the heart in rare cases – something that can be avoided altogether by hitting other parts of the body.

Zipes, who has acted as an expert witness in Taser death cases, said his peer-reviewed paper for the Journal of the American Heart Association documented eight cases of people in the US who have died or suffered significant brain damage following a cardiac arrest linked to a Taser shot.

But, despite the apparent dangers of chest shots, a series of requests under the Freedom of Information Act suggests that police are routinely aiming Taser shots at that part of the body.

Records from Gwent police force, for example, show that 82% of 55 Taser discharges by its officers hit people in the chest. Officers from Lancashire police fired Tasers 186 times between 2009 and October 2012, with 65% of shots hitting the chest.

There have been 10 deaths since the introduction of Tasers by UK police forces in 2004. The most recent was last Wednesday evening after a 23-year-old factory worker, Jordan Begley, from Gorton, east Manchester, was said to have suffered a "medical episode" and died after police fired at him with the weapon.

The chief constable of Greater Manchester, Sir Peter Fahy, and its police and crime commissioner, Tony Lloyd, met the dead man's family and expressed their condolences.

No cause of death has been directly linked to the high-voltage charge emanating from the weapons in the UK. But two of the 10 cases, including last week's death in Manchester, continue to be investigated by the Independent Police Complaints Commission (IPCC).

The Association of Chief Police Officers (Acpo), which is responsible for Taser guidance, told the Guardian that following the 2009 warning, an independent panel of experts re-examined the threat to life from Tasers but found no substantial risk.

Simon Chesterman, deputy chief constable of West Mercia police and Acpo lead on armed policing and Taser use, said that after the 2009 Taser warning Acpo asked the medical panel whether police training needed to be changed. "The answer that came back is that as they've said all along, the risk from the electricity is very low," he said.

Chesterman said the panel had maintained that guidance to this day and it was felt there was no need for police "to adjust our point of aim".

He said: "We don't train them [officers] to go for the chest, we just train them to go for the biggest thing they can see, ie the major muscle groups.

"When you've got a violent assailant who is facing you, coming towards you and you have to make a split second decision whether to use Taser or not, the chances are that clearly you're going to aim for the torso and it may well be that one or both of the barbs will attach within the chest area.

"I'm not saying Taser is a risk-free option," he said, but added: "We haven't had what you could describe as a Taser-related death in the United Kingdom – that's despite the fact that we've been using them for 10 years"

A separate FOI from February found that in 2011 Tasers were discharged 1,371 times in the year ending March 2011, a 66% rise on the previous year.

In a statement to the Guardian, Steve Tuttle, vice-president of communications for Taser International, said that in the vast majority of cases, "the cause of death has nothing to do with the Taser deployments and to date in the UK there are no deaths in which the Taser has been listed as the cause of death".

He said the company's "preferred targeting zones" were "best practices" that "take into consideration the most effective areas for placement on moving and/or violent subjects that don't always co-operate.

"We occasionally modify recommendations and warnings to reflect a best practices approach for our customers to consider," he added. "The release of our [2009] training bulletin should not be interpreted as a significant change in how our products should be used. The recommendations should be viewed as best practices that mitigate risk management issues resulting in more effective deployments while maximising safety considerations such as avoiding face, neck, and chest/breast shots."

In the US, Taser was recently ordered to pay $5m (£3.3m) to the family of 17-year-old Darryl Turner, who died in 2008 after being shot by police with a Taser.

The lawyer in that case, John Burton, from Pasedena, California, said that by aiming for the chest, UK police were being irresponsible.

"This is just so irresponsible. I'm shocked to hear this," Burton said. "If UK cops are shooting people in the chest it just shows that they just don't take things seriously."

Sophie Khan, a UK solicitor who specialises in Taser cases, said Taser's guidance "is meant to be there to protect the public and the police from civil claims".

She added: "From what I see people are being shot in the chest and stomach, when they don't even need to be Tasered in the first place, that's what's happened."