I've had similar doubts Delta82, but the quote above really made me feel more confident that they don't have a leg to stand on.

Had a phone call from Watchdog this afternoon (quite quick since I only filled out the online form last night), the researcher just asked whether I was in the house at the time and if they could use my name when contacting ACS:Law. My letter is ready so I'll be sending it this week.

I'm one of the people that have received a letter recently. Been reading through this thread and the associated links for the last few hours. I've gathered together the links I found most helpful below, hope they help. Personally I've come to the conclusion that the letters are legit, so don't just ignore them. But the IP address alone is not sufficient to prove infringement. I'll be drafting a letter refuting the claims (based on one of the links below). It seems daft to me that you should just pay up (and practically admitting to the offense by signing the undertakings). But I can understand that many people would since the tone of the letter is aggressive. First Watchdog BBC - Watchdog: Davenport Lyons - threatening letters The best link to read regarding the response letter Slyck.com • View topic - DL/ACS:law - I've received a letter, what should I do? The solicitor, Micheal Coyle at lawdit - Law Articles and News - Lawdit Reading Room and What to do when you receive a letter of claim - Copyright Law Articles and News - Lawdit Reading Room Good details from someone at comment #31 here ‘New’ Anti-Piracy Lawyers Chase UK File-Sharers | TorrentFreak