Sussex Police are increasingly turning to volunteers amid major budget cuts.
By December, 471 Special Constables are expected to be working, compared with 240 in 2010.
Their number is set to have increased by more than 88% between 2010 and 2015, compared with a 44% increase across England and Wales.
Meanwhile, the force will have cut 10% of its paid workforce by 2015, as it tries to save £56.8 million. Specials are being given wider roles including investigations, according to an HMIC report.
Mark White, secretary and discipline liaison officer at the Sussex Police Federation, is concerned. He said: “While we are pleased that so many people are giving up their time to be special constables, it is a worry that we are becoming ever more reliant on them.
“They do a fantastic job but with the chief constable announcing that the government tell us we have to save another £50m, we are increasingly concerned that the additional specials simply won’t be enough to fill the gaps.”
Sussex Assistant Chief Constable Robin Smith, however, said volunteers “enhanced the services provided to the community”.
He added: “Special constables have worked in Sussex for over 100 years. Last year, special constables volunteered more than 80,000 hours with us. Their professionalism, commitment and enthusiasm are admirable.”
Specials volunteer for at least four hours a week, and have much of the same training as full-time officers.
Special Constable Matthew Clements, based at Rye, volunteers between 30 and 40 hours a month and said the role was “the best decision of his life”.
He rejected the idea that specials were plugging staffing gaps, adding: “Not at all. They appreciate the extra couple of bodies.”
The HMIC report praised Sussex Police for the way it is dealing with budget cuts.
It said the force had tried to limit cuts to its workforce and increase the proportion of those working in visible roles, adding finances were “well-managed”.