The Ministry of Sound has abandoned plans to prosecute hundreds of BT customers thought to have illegally downloaded music after it emerged the telecoms company has deleted 80 percent of the necessary data.

The record label has employed the services of legal firm Gallant Macmillan and was seeking a court order that would see BT-owned ISP PlusNet, as well as Sky and Be Broadband, forced to hand over the names and addresses of web users thought to have illegally downloaded tracks, for which the Ministry of Sound owns the copyright.

BT initially deferred the court case until it could be reassured the data would have been stored securely. BT's request came on the back of a DDoS attack on legal firm ACS:Law, which resulted in the names of web users thought to have illegally file-shared being leaked to the web as they were not stored securely. Details of around 500 PlusNet customers were contained within the data leaked to the web.

Once Gallant Macmillian has obtained the details it planned to issue those suspected of illegal file-sharing with warning letters that state the recipient must pay a fine and sign a legal undertaking agreeing not to illegally download in the future.

However, BT has now revealed that it deleted 20,000 of the 25,000 details in a bid to comply with its data retention policy, under which data is held for just 90 days.

"Upon request from Ministry of Sound, we saved as much of the specific data sought as we reasonably could and any not preserved must have been too old," a spokesman for BT said.

"The Ministry of Sound and its solicitors are well aware of this."

Ministry of Sound CEO Lohan Presence said that the record label was disappointed, but it would not continue with the court case.

"Given that less than 20 percent of the names remain and BT costs have soared from a few thousand pounds to several hundred thousand pounds, it makes no economic sense to continue with this application," he said.

However, Presence added the Ministry of Sound is "more determined than ever to go after internet users who illegally upload our copyrighted material".

"We will be making further applications for information from all ISPs."