"Gagging orders" have been issued to thousands of UK council workers as part of their payoff agreements, figures obtained by the BBC suggest.

Figures showed 17,571 settlement deals had been signed between 2010 and 2015, many including confidentiality clauses.

Cardiff Council has issued the most settlement agreements, with nearly 3,000 employees signing one since 2010.

The Local Government Association (LGA) said councils only made special payments to avoid costly legal action.

The government said guidance made it clear that confidentiality clauses should only be used in "extreme circumstances" - and not to hide the value or nature of any severance payments.

But the guidance is not binding and there is no legal restriction preventing local authorities from using them.

Image caption Meg Hillier, chairwoman of the Public Accounts Committee, is concerned about the use of "gagging orders"

In 2014, government spending watchdog, the Public Accounts Committee, highlighted the use of the agreements across the public sector and called on the government to monitor and curb their use.

Committee chairwoman Meg Hillier told the BBC she was concerned they were being used indiscriminately by some local authorities.

"There can be no excuse for silencing people who've got a legitimate concern," she said.

"If an employee is being told they can't talk about something and bought off, that's not an acceptable use of these settlement agreements."

Enhanced payouts

The 5 live Investigates programme made a Freedom of Information request to all 433 district, city, county and regional councils in the UK. 70% responded. The responses revealed that 17,571 workers had signed a settlement agreement between 2010 and 2015.

Staff often received an enhanced pay-out for signing such an agreement. But it is unclear how much these enhanced arrangements are costing the public purse because the figures include money that staff would have been entitled to under their normal terms and conditions.

But the 17,571 settlement agreements resulted in pay-outs totalling £226.7m.

The City of Cardiff Council issued the most, totalling 2,008 and resulting in pay-outs totalling £5.5m.

Cardiff, and a number of other councils, had been using them as a matter of routine.

The council said that policy ended in January 2015 - and had been used to protect it from legal claims. It said by making enhanced payments it was able to get more people to volunteer for redundancy and that would bring savings.

Wirral Council used the agreements with more than 1,000 people who took voluntary redundancy or early retirement between 2010 and 2012 - although they said they were rarely used now.

Sunderland City Council used them 155 times in the financial year 2014/15 - but said they were used to protect confidentiality and not to stifle criticism.

'I was gagged'

Vanessa Hewitt, from Kent, worked as a chef for Swanley Town Council before opting to take voluntary redundancy last year.

"I was totally confused because they wanted me to sign this agreement before they gave me my redundancy.

"In the agreement it says I should not discuss this agreement with anybody, I must not speak to the press, I must not discuss or make reference on Twitter or Facebook. Basically, I was not to say anything to anybody… the union rep said this was a gagging order.

"It leaves me with the question, why did they want to gag me?"

She refused to sign the document, although she was still able to receive her redundancy package.

Swanley Town Council said agreements were entered into voluntarily and allowed people to leave on mutually-agreed terms. It acknowledged it was common for agreements to contain clauses to prevent either party from saying anything negative.

A spokesman for the Department for Communities and Local Government said confidentiality clauses should not be used to "stop, stifle or control individuals from speaking out about concerns about their employer".

"There is no excuse for outrageous payoffs at a time when all parts of the public sector should be finding ways to save taxpayers' money," he added.

The LGA, which represents local authorities in England and Wales, said enhanced payments were only made in "extreme circumstances".

"It is also important to note that when calculating payouts, local authorities are one of the most efficient groups in the public sector," it said.

A government report into the so-called Trojan Horse scandal in Birmingham in 2013 found that head teachers who were raising concerns about governing bodies that were trying to introduce strict Islamic principles in some schools were offered settlement agreements so they could be removed from their jobs.

One head teacher told the BBC: "The inquiry exposed that Birmingham [Council] let me and my colleagues down. All I can conclude from that is that I actually became the problem because I was complaining too often and they could deal with me rather than actually dealing with the whole issue and exercising their duty of care to me."

Birmingham City Council said it had reviewed the agreements and "they were the right thing to do at the time".