Top secret ... so why did council post details of high security spy centre on the internet?

Details of one of Britain's most sensitive spy centres have been revealed in official documents posted on the internet by a local council.

Whitehall security officials have raised serious concerns after the authority published a planning file revealing the 'national security' role of the development.

The major blunder means that the full details of what is believed to be a covert MI5 operations centre - used to share intelligence with MI6 and GCHQ - are now in the public domain.

The documents include plans of the building and details of its sophisticated 'anti-intruder measures'.

They also reveal sensitive information about the number of staff - including security guards - who will work at the spy centre, as well as its hours of operation and the location of all its security cameras.

Diagrams in the planning file show banks of computer servers, which are understood to form part of a system designed to speed up intelligence-sharing between Britain's security agencies.

The project was designed to disguise the giant computer hub by hiding it in an anonymous-looking warehouse in the South-East of England.

But the documents published by the council - which The Mail on Sunday has decided not to name for security reasons - show photographs and maps of the building and leave little doubt over what it is being used for.

Emails from the planning officers involved in the decision to give the go-ahead to the massive development also demonstrate the site's importance to national security.

A message from a part-time worker in the council's planning department explains the sensitivity of the site.

Incredibly, this discussion has been published on the internet. More