DoT - As I mentioned, I'm not familiar with either UK law, so I could be wrong. But I didn't see anything in the 13 year old thread indicating that using the house to house forms would be illegal (other than speculation). In the more recent thread, it warned about passing the information along to others.
I hadn't contemplated that as my recollection from my time in was that the notes would generally be for personal use only. But now that I think about it, I do remember some JWs passing off supposedly interested persons to others. That probably does explain their discontinuation. But I don't think it would be illegal to use the forms for one's own personal field service use. Obviously many JWs don't listen, so they may have discontinued them out of caution for that reason.