The number of special constables serving with Thames Valley Police has almost halved during the past three years.

The number of specials -- volunteer officers who work on a part-time basis -- has fallen from 656 in March 1997 to 369 in March this year, and fewer than 350 now.

Henley Conservative MP Boris Johnson, who obtained the figures, said: "Special constables play a vital role in neighbourhood policing. But specials, like full-time officers, are being overwhelmed with bureaucracy and paperwork.

"Morale across the police has plummeted.

"Disenchantment and frustration have led to a huge retention and recruitment crisis as these figures show."

Thames Valley Chief Constable Peter Neyroud said special constables were trained to work alongside full-time officers on the front line, when previously they might have been in support roles.

He said the thought of being on the front line could have discouraged people from becoming a special but said volunteers were welcome in other roles such as manning small rural police stations.

Mr Neyroud added that numbers were also low because special constables had become full-time police officers, of which there is a shortage in the Thames Valley.

"I make no apologies for that," he said.

Thames Valley Police wants to make the role more attractive, by paying special constables about £950 per year to work increased hours on specific initiatives.

The force's special constables have full police powers, but receive just travel expenses.

If a pilot scheme in the south east of the area is successful, payment could be extended to Oxfordshire.