More officers from Merseyside Police are now able to use Taser stun guns as part of a 12-month trial.
Tasers disable a suspect with an electric shock
Concerns have been raised for public safety as the Taser guns have been made available to more officers in 10 forces across England and Wales.
Police who are not firearms-trained can now use the 50,000-volt guns to protect themselves or the public.
Amnesty International said officers using the weapons in the one-year trial may not have been properly trained.
The Police Federation said Tasers were becoming necessary on the frontline.
Until now, about 3,000 Tasers had been issued in Britain, but only to members of police firearms units.
Firearms officers could only use them when confronted by an armed attacker, but their powers were extended in July to include incidents of severe violence or threats.
Other forces taking part in the trial are Avon and Somerset, Devon and Cornwall, Gwent, Lincolnshire, Metropolitan Police Service, Northamptonshire, Northumbria, North Wales and West Yorkshire.