Strathclyde Police is set to axe nearly 600 jobs among its support staff.

The force aims to begin a programme of voluntary redundancies as early as next month.

But fears have been raised that frontline police could be forced to to plug the gaps by doing jobs normally done by support staff.

The move to axe jobs is part of plans to slash spending, which could also see officers’ benefits, such as overtime pay, being hit.

Union leaders said they believed the force was seeking to cut 600 jobs – almost one in four – among its 2700 civilian workers.

Chief Constable Steve House will next week ask a full meeting of his ruling police authority to approve the voluntary redundancies.

Mr House set a chilling tone ahead of negotiations with a circular e-mail making it clear jobs – and terms and conditions, such as overtime and extra payments for working unsocial hours and cash bonuses for being on duty during public holidays – were on the line.

He wrote: “I have to warn you that when I say the cuts will be significant, I am not being unnecessarily dramatic.

“We won’t know the precise scale of the cuts until November, but even if they are at the low end of our projections, it will still mean we will not be able to afford to employ the amount of people we currently do.”

The force has already imposed a freeze on all recruitment and last month it said it was exploring ways of getting rid of some veteran officers.

But Stephen Curran, the Glasgow councillor who chairs the Strathclyde Police Authority, said: “We have to look at how we end up with a sustainable policing service.

“We have to watch out, for example, that by cutting the numbers of support staff we don’t end up having uniformed officers taken off the frontline to do desk jobs.”

Gerry Crawley, of civilian staff union Unison, said: “We have information they are going to get rid of around 600 support jobs.

“There is no way they are going to be able to do all that using voluntary redundancy. I think we are also going to see police office closures across Strathclyde because of this.”

Les Gray, chairman of the Scottish Police Federation, said: “We will be deeply concerned if our members end up behind desks because their civilian colleagues go. We believe police cuts will end up costing the public purse as we will see higher crime and more disorder.”