SCOTLAND's chief constable Sir Stephen House has warned of a funding threat to frontline policing and raised the prospect that former divisional headquarters may be sold.

Sir Stephen, who needs to plug a multi-million pound black hole in his £1bn budget, said he would do whatever he could to make savings away from the frontline.

In an interview with The Herald, Sir Stephen, who is due to step down next year at the end of his contract, gave his clearest hint that it would not be possible.

He suggested Police Scotland's already stretched overtime budget may have to be "looked at again".

Sir Stephen, who has been under fire over stop-and-search and armed policing policies, has already said "extreme measures" are required to save money.

He said: "You are starting to get to a situation where there may be some operational impact."

However, he believes potential savings to back office functions that could prove a major political headache for his successor.

Sir Stephen warned Police Scotland may have to sell the former HQs of old forces in Inverness, Dumfries and Glenrothes, Fife, where back-office staff are based, relocate some town police offices in to council buildings; and make further cuts to the number of 999 control rooms, already going down from 11 to four.

The national force has already come under pressure for alleged "centralisation" and any further cuts to local back office functions will meet stiff resistance.

Sir Stephen, however, stressed his proposals were "only thoughts and ideas at the moment" and that it would be up to his ruling board, the Scottish Police Authority to make final decisions.

But he stressed the financial crisis was such that it could not shy away from controversial decisions.

He said: "The tendency for a public agency to take it easier on a change process in the run up to elections at such a politically sensitive time. "The reality is I am not sure we can afford to do that. We have to balance the budget."

Long-term plans to sell old force divisional bases or share offices with councils or other public-sector bodies are unlikely to deliver the kind of savings Sir Stephen needs in 2015-2016, a crunch year.

Police Scotland in its first two years saved more than the budget of three of its predecessors, the old Northern, Dumfries & Galloway and Central Scotland forces.

It has to find another £58m in savings by the end of the current financial year. Sir Stephen and his team have only earmarked £47m.

It is the remaining unidentified £11m that is sending a chill through his ranks.

Sir Stephen stressed he could not, and did not want to, breach the SNP's commitment to keep officer numbers above 17,234 officers. It is 1,000 more than the party inherited when they took power before the economic downturn in 2007.

Referring to the 17,234 figure, he said: "It does mean that much of the savings has to come from something other than police officers.

"That takes us to buildings, vehicles, contracts, procurement. And it takes us to police staff.

"We have very little leeway in terms of not balancing the budget.

"We are reducing the number of control rooms down to four. Could we reduce it even more?"

"We are talking to virtually every council in Scotland about co-location because in some areas our police stations are not in the right place.

"Take Dumbarton, its station is on the wrong side of a busy dual carriageway.

"It would be far preferable for us to have a building in the town centre and it would make sense to co-locate that with the local council."

"In some towns we have an HQ for a legacy force and an operational police station within a couple of miles of each other. Do you need both buildings?"

Sir Stephen cited what he called "good examples" of this in the old Fife, Dumfries and Galloway and Northern Forces but he stressed there were "no immediate plans" to shut old HQs.

His operational budget will depend on many things beyond his control, such as whether Rangers wins promotion to the top flight.

He said: "We have spent less on football in recent years because we have not had the seven annual Old Firm clashes that we had towards the end of Strathclyde time.

"We have spent less because Celtic and Rangers have been split up through the vicissitudes of sport."

Police Scotland is also saving money because there are fewer homicides, requiring fewer resourcs to be assigned to costly murder investigations. But the forces is paying out more because of its policies the chief constable has introduced to encourage more rape reports.

Sir Stephen stressed he would not cap spending on major investigations.