I've just been talking to TalkTalk about moving my broadband to them and they say I don't need a MAC key. However, at PlusNet it says that a cessation charge of £25 will be made if I move without supplying my MAC key. I don't know who to believe. I don't want to risk having to pay a cessation charge as a result of not having a MAC key.
Providing you're moving to a LLU provider i.e Talk Talk you don't require a MAC, only if you were to remain on the BT network or move to a shared LLU. You'll not be charged the cessation via either if you move to a LLU provider as explained here.