Public sector staff are suffering "unprecedented anxiety and concern" over the fragility of their job security, after latest statistics revealed one-in-six council jobs are being axed.

According to statistics released under the Freedom of Information Act, 5,351 council posts were lost between January 2010 and January 2012 – including a quarter of all positions at one local authority.

Regionally, it represents a 17.2% decline in staff numbers at the 12 largest councils in Devon and Cornwall, not including school-based employees.

Stuart Roden, regional organiser of public sector union Unison, said council employees who had survived previous austerity measures were increasingly fearful about the longevity of their current employment.

Mr Roden said: "We are getting a letter every day [from some public sector departments], saying they are really under pressure.

"Staff are completely in despair. There is a lot of anger and disempowerment."

The greatest decline has been at Devon County Council, where more than a quarter of jobs were shed in two years. In total, 2,591 of 9,529 employees were lost from the council, a drop of 27.2%.

By comparison, Cornwall Council, which has a similar operating budget, saw its staff numbers fall from 10,354 to 9,301 in two years – just over 10% of its workforce.

In total, the number of council staff across Devon and Cornwall fell from 31,095 to 25,744.

A Devon County Council spokesman said only frontline vacancies had been filled since November 2009, in an effort to reduce redundancies.

He added: "A large proportion of the reduction of our staff numbers is due to a combination of structural reform which has led to staff being transferred to external agencies.Devon has reduced its workforce by almost 1,800 posts as a result of this jobs freeze, and further restructuring means we're likely to see further reductions, but not on the same scale."

A statement from Cornwall Council also said the decrease in staff numbers was due to restructuring, as well as the amalgamation of seven councils into one, in 2009.

The statement said most of the job losses were through voluntary redundancies. It added: "The council worked hard to limit the number of redundancies through not replacing non-essential employees when they leave, filling essential posts through the use of agency workers to ensure that vacancies are available for the redeployment of employees at risk of redundancy and by the successful redeployment of a significant number of 'at-risk' employees.

"As a result the majority of people leaving the authority on the grounds of redundancy have been voluntary leavers."

The council said at least 600 employees had "transferred" to other organisations.

Mr Roden added: "The fact is that thousands of jobs have been lost in the public sector in the region, and that has an impact on town and city centres. You only have to look at the empty shops to realise the money just isn't there anymore."