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 former prime minister made the comments as he prepares to return to politics saying he wants to be "part of the debate" on Brexit.
The new measures would mirror childcare vouchers and see workers sacrifice some of their salary to benefit.
Google, Facebook and Twitter could face multi-million pound fines over their failure to remove illegal content, MPs say.