Some 256 local authorities have signed more than 4,000 ‘gagging orders' to prevent former staff speaking out, a Freedom of Information campaigner has revealed.

Research undertaken by Paul Cardin, a whistle-blowing former employee at Cheshire West and Chester Council shows the number of confidentiality agreements signed between council employers and staff increased nearly sixfold from 179 in 2005 to 1,027 in 2010.

In all some 4,562 compromise agreements, many of which customarily contain confidentiality clauses, have been signed with former staff, Mr Cardin's survey discovered.

Brighton and Hove City Council was recorded as the most prolific authority, signing 123 agreements with exiting staff, followed closely by Bristol City Council, which signed 121 and Coventry City Council with 114.

Kent CC has made 95 agreements, including one for former managing director Katherine Kerswell who received a £420,000 settlement to leave after less than two years in the job. 

Ms Kerswell is now director of civil service reform at the Cabinet Office, and a separate survey undertaken by The Daily Telegraph has uncovered Whitehall departments spent around £14m on similar agreements with more than 200 civil servants.

Communities secretary Eric Pickles wrote to councils in February stating all severance payments of £100,000 or more should be subject to a full vote at council meetings.