THERESA May has launched a stinging attack on the the decision to merge Scotland's eight police forces into one.

The Home Secretary said top-down mergers like Police Scotland's do not generate promised savings, lose local accountability and cause unnecessary complexity that distracts from crime-fighting.

But the SNP administration hit back, accusing Ms May of “the height of hypocrisy”, saying how she was presiding over a collapse in police numbers in England and Wales amounting to tens of thousands of officers while it had maintained 1000 additional officers in the face of Westminster cuts.

Niven Rennie, President of the Association of Scottish Police Superintendents, said the Tory politician's comments were “a pretty low shot” aimed at the police.

Speaking at the annual conference of the Police Superintendents Association of England and Wales, the Home Secretary emphasised the need for further efficiencies, noting how some people still argued that the only way to deliver savings south of the border was to restructure the 43 forces.

But she stressed the success of local collaboration was evidence that big, top-down restructuring was not needed.

“And,” she told senior officers, “if you need further proof of the risks, I would urge you to look north of the Border.

“There, the top-down merger of eight forces into a single force, Police Scotland, was once heralded as the future of policing but is already facing difficulties.

“Despite being first announced in 2011, and formally created in April 2013, there is still no full business case for Police Scotland and the outline business case that has been published suggests that it will take 15 years to deliver the promised savings.”

Mrs May noted how last week, “after a series of high profile issues”, the SNP Government announced a review into the way Police Scotland was governed and held accountable to communities.

“In an admission that local accountability was lost in the merger and is now having to be restored, the new chief constable has been ordered to attend local ‘public scrutiny sessions’ in the same way local chief constables are held to account in England and Wales,” explained the Home Secretary.

She maintained the evidence from Scotland was clear. “Top-down restructures in policing do not generate the savings they promise. It can cause unnecessary complexity that distracts from the day to day business of fighting crime. And in the process, the most precious element of our system of policing by consent - local accountability – can be lost.”

She added: “Instead, we must go further to drive deeper collaboration, better sharing of back office services and a more intelligent approach to where police capabilities sit to generate savings without the loss of local accountability and identity.”

But a spokesman for Michael Matheson, the Scottish Justice Secretary, told The Herald: “This is the height of hypocrisy from Theresa May. She and her party are presiding over a total collapse in police numbers south of the border, which are predicted to fall by a further 20,000 – on top of the 15,000 already lost – to their lowest levels in 40 years.”

He stressed that, in contrast, the SNP Government had maintained 1000 additional officers in the face of Westminster cuts, helping crime in Scotland to fall to a 41-year low.

“The reality is that great progress has already been made towards the police reform savings target of £1.1 billion by 2025/26 with around £880 million of recurring savings already delivered,” added the spokesman.

Of late Nicola Sturgeon, the First Minister, has acted to end a series of rows over Police Scotland with an effective "reset" for the force.

Mr Matheson has named a new watchdog for the organisation, ended controversial "consensual" search and put call centre closures on hold.

The moves came after Chief Constable Sir Stephen House said he would stand down early, meaning the force will soon have an entirely new uniformed and civilian leadership.

The Justice Secretary announced the policy changes in Holyrood after an independent report said abolishing consensual searches would not leave a serious gap in law enforcement.

He also accepted the recommendations of another independent report by Derek Penman, HM Inspector of Constabulary, into call centres following the fatal M9 call centre mistake.

Mr Rennie said: "She doesn’t really know what the issues are in Scotland.

“The biggest issues we are trying to deal with are from budgets we have which stem from austerity measures from Westminster, from her party.”