Essex police has been criticised for its move to hire "volunteer detectives".

The force revealed earlier this week it was advertising for two unpaid special constable roles to support detectives in the Serious Crime Directorate.

A job post on the force's website asks: "Do you want to help investigate the most serious crimes in Essex including murders, attempted murders, stranger rapes and kidnappings?"

"Working alongside detectives, you'll receive training to help you bring justice to some of the most serious criminals in Essex."

The creation of the new roles has been called "unacceptable" by critics, but Essex Police deny it represents "policing on the cheap".

Labour councillor Dave Harris, of Colchester Borough Council, said he was "absolutely appalled" by the force's move.

"It's the thinnest blue line I've seen in my life," he said.

"The volunteers have good intentions but they are going to make mistakes. It's just not right. It takes years to train these professionals."

Colchester council's public safety boss Mike Lilley, said volunteers do "fantastic" work, but the latest move was "not an ideal solution".

"Austerity has basically handed the streets over to commit crime," he said.

"All the police are doing is trying to play catch-up.

"If you go into the police station, it's the Mary Celeste at times, the officers are hardly there.

"We want to see police who are trained at the police college and trained in all aspects of police work."

Karen Stephens, secretary of the National Police Federation of England and Wales Detectives' Forum, said: "We cannot ignore that there is a crisis in detectives within policing, with a serious shortfall in the numbers of detectives seen throughout England and Wales."

She said Essex Police's recruitment of volunteer detectives was the "first of its kind" but not "surprising".

"Forces across England and Wales are struggling to cope with minimal numbers and results from our National Detectives Survey show that detectives feel overworked and overwhelmed, with morale at rock-bottom and a staggering number taking sickness absence caused by exacerbation at work," she said.

"Being a detective was always a sought-after, desirable role; however, this is no longer the case."

She added: "Whilst these volunteers wouldn't be expected to carry out the same role as a trained detective and are not to take the place of a trained detective, the lower level basic support they may be able to give overstretched detectives can only be a positive thing as long as they have the adequate training and support in place."

Essex Police Assistant Chief Constable Nick Downing said: "This is not about policing on the cheap or lowering the status of detectives."

He said the force continued to invest in training detectives and that special constables were a key part of the "policing family".

"It may be the case that people hoping to join us as a special constable within the Serious Crime Directorate could bring specialist skills from their everyday professional life which could be really beneficial to this specialist area of policing," he added.

"It may be that someone enjoys their day job but is looking for an exciting challenge that enables them to give something back to the community.

"Or someone may be interested in a career in policing but they want to find out what it is like before they make that commitment to joining, volunteering as a special constable allows people to have the best of both worlds."