The ISP complained about the way the issue was raised in the press, and insisted that the BPI had only provided evidence for one of the 17 IP addresses.
Tiscali claimed that it routinely cooperates with the music industry and does not condone illegal file sharing or any other abuse of its service.
However, Tiscali maintained that the press release put out by the BPI was not the way to resolve the issue.
"As you will already be fully aware, Tiscali will not be able to disclose customer details to you unless you obtain a court order requiring us to do so," Tiscali's letter to the BPI said.
"To disclose without a court order would put Tiscali at risk of breaching the terms and conditions of its customer agreements, and the provisions of the Data Protection Act 1998."
Tiscali stated that any legal implications of its investigations would need to be handled by the BPI when it had obtained those customer details through the proper channels.
"It is a matter for [our customers] to decide whether they wish to enter into such undertakings or defend proceedings against them in the courts," the letter said.
"It is not for Tiscali, as an ISP, nor the BPI, as a trade association, to effectively act as a regulator or law enforcement agency and deny individuals the right to defend themselves against the allegations made against them."
Tiscali said that the BPI had provided a list of 17 IP addresses with dates and times of use and a list of sound recordings, including screenshots of the shared drive of one customer.
"You state that such evidence is 'overwhelming'. However, you have provided no actual evidence in respect of 16 of the accounts," said Tiscali's letter to the BPI.
"Further, you have provided no evidence of downloading taking place nor have you provided evidence that the shared drive was connected by the relevant IP address at the relevant time."
Tiscali said that it had contacted the customer about whom the BPI had provided 'evidence' and given that person seven days to provide an explanation.
"Should we not receive an adequate explanation during such period, we shall suspend the user's account pending resolution of your investigation, assuming by that time we have received evidence from you of a link between the user account and the IP address at the relevant time," stated the ISP.
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