Buckingham Palace's State Dining Room has been closed for six months over safety fears.
The ceiling in the room - where Queen Elizabeth broadcast her Christmas speech from last year - was found to pose a danger to the royal family, and as a result six other rooms which could be affected, including The Ballroom, are being inspected by engineers.
The source said: "The State Dining Room is out of service for six months. They are checking the shared roof cavity above six State Rooms."
This will come as a blow to the queen as the room will not be available for the 89-year-old monarch's annual Diplomatic Reception, in which she invites 1,500 of the country's top diplomats to the Palace.
A second source revealed the Palace - which has 775 rooms - has been talking to the Treasury about how any potential repairs to the State Room and other areas of the 300-year-old house could be funded.
A Palace spokesman told the Mail on Sunday newspaper: "As the result of a routine survey an issue was found with one of the ceiling beams in the roof space of the State Dining Room.
"Following further assessment, access to the room has been suspended."