Britain's Ministry of Defence has racked up a STG40,000 ($A69,625) bill on telephone calls to the speaking clock despite a ban on employees using the service, figures reveal.

The ministry introduced the ban on using the service, which has been running since 1936, in 2012 and urged employees to use free internet sites in order to get the exact time.

In spite of the directive, the ministry received a telephone bill of STG18,804 just in 2012.

It has made 130,000 phone calls to the service since the ban was introduced.

"A ban was introduced to our newest telephone network, but due to a technical error ... there has been some inadvertent spending on the speaking clock which has now been stopped," said a ministry spokesperson on Friday.

AFP