TRADE unions are to challenge swingeing cuts to Police Scotland in the wake of the M9 incident in which a couple were left in a crashed for three days despite the alert having been raised.

Unison, which represents civilian workers within the force, is due to meet with senior police figures on Monday when it will raise the M9 incident.

The case shocked the country as it emerged John Yuill, 28, and Lamara Bell, 25, lay for three days before being discovered after coming off the road near Bannockburn outside Stirling while returning from a camping trip.

A call was made to Police Scotland but not followed up. Chief constable Stephen House has said he will not resign over the deaths, maintaining that police reforms were not responsible for what happened.

All Scotland's eight police forces were merged in to one two years ago in a bid to save tens of millions of pounds in the long term.

Police Scotland and the Scottish Police Authority have now also said that the coming cuts will be "the most challenging to date" with savings from duplication - one of the key reasons for creating a single force - already exhausted.

The Scottish Police Federation, which represents rank and file officers, said its analysis shows that there has been an increase in police staffing costs that is swallowing up budgets.

It claims Police Scotland is shedding civilian staff to reach politically set targets of policing which included 1,000 extra officers.

Unison claims cuts of £57 million over the next two years will lead to the loss of 400 more jobs in the year ahead and 600 the following year.

Around 1,500 posts have been cut since Police Scotland was formed two years ago.

George McIrvine, Unison branch secretary for police staff, said he believes employee shortages had been behind the incident being investigated by the Police Investigations and Review Commissioner and Her Majesty's Inspector of Constabulary in Scotland, and that further cuts could lead to similar tragedies in future.

Mr McIrvine said the Union has “from day one always said there is a tragedy waiting to happen”.

He said: “The Scottish Government has got to take some responsibility.”

The SPF said the investigation should look closely at budget factors.

Calum Steele, General Secretary of the Scottish Police Federation, said: “Eight years ago 80 per cent of the budget went on staff and associated costs, broken down to 60 per cent police staff and 20 per cent civilian.

“As a proportion of the budget now, staff and associated costs are 90 per cent and that breaks down to 60 per cent police and 20 per cent staff.

“That is 90 per cent of the budget gone before a light is turned on in an office.

“This places a tremendous pressure on the service.”

A Scottish Government spokeswoman said: "Crime in Scotland is currently at a 40-year low, supported by the 1,000 extra officers we have delivered compared with 2007.

"It is not appropriate to prejudge the results of the ongoing, live Pirc investigation or the HMICS review."

A spokesman for the SPA said: "Both the SPA and Police Scotland acknowledge the huge contribution that our workforce have played in delivering that (cost reduction), and that it has not been achieved without some pain.

"In approving the budget for the current year, we were clear that this would be the most challenging year to date with many initial savings from duplication already exhausted and some of the future benefits of investment in new technology still ahead of us.

"We have been open and up front with staff that voluntary reductions in the workforce will be part of that, but they will not be the only area looked at."

Detective Chief Constable Rose Fitzpatrick said: “Police Scotland has met its budget requirements in the first two years of the single service and we recognise that the years ahead will be extremely challenging financially."