My understanding (given the billions of courses in Data Protection I've had to attend) was that it's not illegal to record a conversation without someone's permission (unless you're going to use it to blackmail, or publish without their consent the contents of said conversation).
In our call centre section, there is a recorded message that all calls are recorded before the caller gets through. This way the call is admissable as evidence in court - obviously Ethel's link shows a newer ruling, but again, every individual case is taken at it's own merit.
I've recorded family get togethers (covertly) for my family tree research - obviously this is personal use and will not be published, but I have gleaned info that would not really be appreciated if it got out. I think it will depend on your motivation for taping the event really