The disc, which was lost in December, contained information including names, salaries, national insurance details and bank account numbers. It was an encrypted optical disc.
The disc was sent by "the usual secure TNT courier service", a spokesperson at the British Council said, but it had not been received by the department's human resources staff who were expecting it.
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"TNT has informed us that they are still taking steps to find the disc," the spokesperson said. "The data only included staff records and no information about external British Council contacts is involved."
The British Council has ordered an investigation into data handling. A spokesperson at TNT told PC Advisor's sister title Computerworld UK the firm was still looking for the disc, a month after the loss.
Last June, TNT was blamed by the government for losing a Scottish Ambulance Service disc containing the details of nearly a million emergency calls.
The loss was originally revealed by Liberal Democrat home affairs spokesman Chris Huhne, who said it was "clear that Whitehall's culture of carelessness about confidential data has not ended".