London, June 14 : A construction company that built the headquarters of one of Britain's most sensitive spy bases - MI-5, has inadvertently revealed some of its well kept secrets on the Internet.

The publicity brochure placed online contains the address and full colour pictures of its northern operations center, reports The Times.

The building was opened amid great secrecy last year. It was used as a base for Operation Pathway, when 12 terror suspects thought to have been planning attacks on shopping centres in Manchester, were arrested. They were later released for lack of evidence.

Though MI5 has been happy to acknowledge the existence of its headquarters in London and Northern Ireland, they see the latest disclosure as major security blunder as they were keen to keep the location of this spy base under wraps to review intelligence failures leading up to the suicide bombings in London on July 7, 2005. (ANI)