This might be significant

[Nodge]

http://www.consumerfocus.org.uk/news/high-court-sets-precedent-after-four-years-of-speculative-invoicing-for-alleged-copyright-infringement
The above link details a high court ruling where a group of pornographic film producers requested O2 (a UK ISP and mobile phone provider) to disclose details of customers whose IP addresses had been linked with illegal file downloading, with a view to sending out speculative invoices. Although this was largely a privacy issue, the court did comment on the nature of speculative invoice letters ...
"The verdict also states that any claim letter sent by copyright-owners or their representatives must properly safeguard the legitimate interests of consumers, particularly those who are innocent of wrong-doing.2 This has big implications in restricting the ability of such companies to send out threatening ‘Pay now – or else letters’, as was also seen in the recent high profile case of ACS Law. The High Court will in a separate hearing impose conditions on the wording of the order and the letters"