This might have been publicised, but I used 1471 this morning and just happened to hear (usually either hang up immediately or dial 3) the fact that if you do use the 3 call the number back there is now a charge.
Googled it and found here that as of yesterday the charge is 6p (there's no charge if you hang up and ring the number yourself). Worth keeping a pen near the phone at all times!
Also ringback requests now cost 15p.
(Public Service Announcement! )