Quite a few years ago I was getting my ADSL BTw broadband from Tiscali and line rental from BT retail. I was notified (perhaps warned?) by Tiscali that TalkTalk would be taking over the line because Tiscali were ceasing broadband provision in the UK. Rather than risk the chance of TalkTalk full LLU (my exchange was TalkTalk LLU enabled at that time) I got a MAC (Migration Authorisation Code) from Tiscali and migrated to another BTw broadband provider. If I hadn't got a MAC and migrated then I could have been automatically transferred to TalkTalk full LLU without my specific authorisation for the move.
A "sorry you are leaving" email and/or letter from the losing provider seems OK, if one is intending to migrate these days, but I do like the idea of the additional requirement for a MAC as well.
BTW I was a very satisfied Tiscali ADSL customer at the time and it was a pity that I had to move
Edited by 4M2 (Mon 16-Nov-20 00:25:33)