More police are now able to use Taser stun guns in the line of duty.
Non-firearm specialists in 10 forces across England and Wales are to be permitted to use the 50,000-volt weapons to protect themselves or civilians.
However, fears have been raised that the one-year trial could compromise public safety if it is not carefully handled.
Liberal Democrat home affairs spokesman Nick Clegg said the pilot projects had to be conducted with "great caution and rigour".
"Whilst everybody understands that police officers need to protect themselves in those places where they feel under direct threat, no-one wants to see us move down the slippery slope to fully armed US-style policing," he said.
"There remain many questions about Taser gun technology which must be carefully weighed up."
The Home Office insists officers will undergo a rigorous selection procedure before being allocated Tasers. Previously around 3,000 were in use, but only by members of police firearms units.
The Tasers deliver powerful electric shocks and are intended to be a "less lethal" alternative to regular police weapons.
