Private security officers are being drafted in to guard crime scenes and free up bobbies for front-line duty.

Sussex Police is the first force in England and Wales to contract out the work and others are expected to follow suit.

Officers from Guildford-based security firm Evensure Management have been available on immediate notice 24-hours a day every day to guard scenes in Sussex since last Monday.

The idea of private firms taking over police roles has met with resistance in the service but there have been no attacks on this move so far.

Brian Cook, the force's scientific support manager, said: "Guarding a scene can sometimes tie up two or three officers who are just standing on street corners doing very little.

"Our highly-trained police men and women will be better employed elsewhere. This fits in with the Home Office push to get more bobbies on the beat."

He said it would not be appropriate to bring in private guards for some major inquiries, such as the Sarah Payne case.

The force has helped with special training for Evensure staff, who wear distinctive identity badges with the words Crime Scene Protection Officer.

They carry mobile phones to call police if there is trouble.

George Paton, Evensure's marketing director, said: "There are lots of people waiting to see how this pans out."

Evensure officers would be "low profile and efficient", he said, and would carry "go-bags" containing special footwear to protect against forensic contamination.

Inspector Graham Alexander, spokesman for the Sussex branch of the Police Federation, supported the idea of relieving police officers from a time-consuming job.

He complained there was no co-ordinated approach to which police jobs should and shouldn't be contracted out.