Sensitive documents have reportedly gone missing from MI6's headquarters.
More than 100 papers relating to layout and security measures of the Vauxhall Cross, south London building vanished.
Building firm Balfour Beatty's contract to refurbish the building was terminated after the documents disappeared, according to The Sun.
The papers are understood to have been drawn up by the construction group and are not believed to have fallen into the hands of hostile powers.
To ensure they did not go missing the documents were supposed to have been kept in a secure room while work was ongoing.
Access was limited to a small number of supervisors.
Regardless, the alarm was raised two week ago when the documents went missing.
A source told The Sun: "The whole building went into lockdown and all the construction workers were kept in isolation.
“To lose such sensitive documents was grossly irresponsible.
“They showed the layout of the building and specifically where alarms and other security measures were. The documents would be gold dust to any enemy agents or terrorists.”
Balfour Beatty declined to comment, while the Foreign and Commonwealth Office, which is responsible for MI6, said: "We do not comment on intelligence matters."
While the documents were not given a Secret or Top Secret classification, they are still considered highly sensitive.
The MI6 building is a prominent feature on the banks of The Thames.
It appeared in the James Bond films GoldenEye, The World is Not Enough, Skyfall and Spectre.
A 50-foot-high model of the building was constructed and subsequently destroyed for Skyfall.
During a special screening of the film at the MI6 headquarters staff cheered when the building exploded.
