Just to echo what Jonni has said, we sent two letters a couple of weeks back - one was a prelim and the other was the DPA SAR.
Both (as far as Royal Mail tracking is concerned) were never delivered. Despite that we still got a response to the prelim (usual 10% offer) but are still waiting on the DPA request (it's only been just over 2 weeks so it's in keeping with the Halifax's heel dragging techniques).
Question is, for the timetable we're working on and the fact that the Halifax put an 8 week period on the acceptance of their partial offers would they still be able to argue they hadn't received the LBA we're sending and believed we were still considering their offer?