The Foreign Office said it was only recently discovered that records of flights passing through an overseas territory used by the US for extraordinary rendition had been lost to "water damage".
A spokeswoman said:
The British Indian Ocean Territory administration is responsible for records of flights on Diego Garcia and they are investigating the full extent of the damage, how many records and what information is affected.
The damage was only recently discovered so it is unknown how exactly or when it occurred.
More top news
The female embryos are named as "Emma" and "Isabella" as the star actress faces an unusual court filing in a long-running custody battle.
Men who have been forced by women to have sex against their will are being urged to take part in a new study into the "hidden crime".
A doctor has lost a Court of Appeal challenge against her gross negligence manslaughter conviction over the six-year-old's death.