Civilian volunteers could be deployed to the scenes of terrorist attacks or to attend cases involving the sexual abuse of children, following major cuts to police budgets and the number of frontline officers.

Earlier this year the home secretary, Theresa May, announced that unpaid staff were to be given police-style powers, including being able to detain a person for 30 minutes or hand out fixed-penalty notices.

It has now emerged that, with 12,000 frontline police officers having left the profession since 2010, the government is refusing to set limits on how volunteers are deployed by forces.

Asked in the House of Commons last week whether their deployment would be limited in cases of child sexual exploitation, serious crime and counter-terrorism, the policing minister, James Brokenshire, revealed that no such bar would be set.

The minister said that volunteers would be deployed only if appropriately trained, but added: “Our consultation on the reform of the roles and powers of civilians and volunteers demonstrated the demand from forces for flexibility in how they deploy volunteer staff, and therefore we should not make assumptions about the operational areas where volunteers can make a contribution.

“These reforms will place the individual decision-making as to which personnel perform which roles firmly in the hands of chief officers, who have the professional expertise and local knowledge to know which powers are needed in their area.”

Brokenshire said it was important not to restrict the operational powers of the police, “who retain the right to deploy staff as they see fit”.

Shadow home secretary Andy Burnham on Saturday accused the government of taking on unpaid civilians to fill the gaps left by budget cuts. There are currently at least 9,000 volunteers working with police forces.

Burnham said: “David Cameron and Theresa May need telling – you simply can’t have policing on the cheap. Just when security concerns are paramount, they have hatched a plan for thousands of volunteers to attend even the most serious cases. Public safety is at risk if the police cannot mount experienced officers in the event of an attack. There’s a proud tradition of the public volunteering with the police, but not replacing them. Labour is calling time on this plan – the government cannot cut the police budget and ask the general public to take the jobs.”

Labour is to ask MPs to block the proposals on the use of volunteers in the upcoming policing and crime bill. The reforms would for the first time see volunteers given powers without becoming special constables, including the ability to hand out fixed-penalty notices, take witness statements, confiscate drugs, alcohol or tobacco and control traffic. They will be able to detain a person for up to 30 minutes but, unlike special constables, they will not have the power of arrest.

The development comes at a sensitive time for the government, with annual crime figures released last week reporting that the murder rate in England and Wales rose by 11% to 573 homicides in 2015. Knife crime also rose by 9% and sexual offences, including rape, increased by 29% to top 100,000 for the first time in 2015, suggesting that a decade-long decline in violent crime is over. Overall crime continued to fall, by 7%, with an estimated 6.4 million offences in 2015.

Earlier this year the chancellor, George Osborne, was rebuked by the UK Statistics Authority for wrongly claiming there would be “no cuts at all in police budgets” in his autumn statement last November.

Sir Andrew Dilnot, its chair, ruled that despite Osborne’s claim to be providing “real-terms protection” for the police, forces actually faced a £160m real-terms cut in their Whitehall funding in 2015-16 and 2016-17.

A Commons analysis estimated that the £160m cut was equal to the salaries of 3,200 police officers over the two years.