The government-funded British Council promotes British culture abroad
A disk containing sensitive personal details of about 2,000 staff of the British Council - the UK's worldwide cultural body - has been lost.
The disk, which was mislaid in December by courier firm TNT, contained names, salaries, national insurance numbers and bank account numbers.
But the British Council said the data could not be accessed as the disk was securely encrypted.
It is the latest in a series of cases of official data being lost.
A British Council spokesman said: "It was sent according to our agreed process with the usual secure TNT courier service but was not received by our human resources team.
"TNT has informed us that they are still taking steps to find the disk.
"The data only included staff records and no information about external British Council contacts is involved."
The disk was not an ordinary CD-ROM or DVD but an optical disk that can only be read by a particular type of reader - but a full investigation of how data is handled at the British Council has been ordered.
The spokesman added: "These precautions ensure that the data is extremely secure in the unlikely event that the disk should fall into the wrong hands. The system for transferring data is being reviewed and in the meantime data is not being sent."
The loss of the disk was revealed a day before the second reading of the Coroners and Justice Bill in the House of Commons on Monday. The act would give government departments more power to share data.
Nov 2007: 25m people's child benefit details, held on two discs
Dec 2007: 7,685 Northern Ireland drivers' details
Dec 2007: 3m learner drivers' details lost in US
Jan 2008: 600,000 people's details lost on Navy officer's stolen laptop
June 2008: Six laptops holding 20,000 patients' details stolen from hospital
July 2008: MoD reveals 658 laptops stolen in four years
Dec 2008: 5,000 nursery-age children's details lost by Leeds City Council
Liberal Democrat home affairs spokesman Chris Huhne, who discovered the loss, said: "Despite the prime minister's assurances after the last data loss on a memory stick in a pub car park, it is clear that Whitehall's culture of carelessness about confidential data has not ended.
"This is another warning that ministers cannot be trusted with the information that they seek on all of us as part of the identity card database."
He added: "It is a curious way for the government to celebrate European Data Protection Day on Wednesday."