Thing is, I rang the cancellations line and explained that I want to leave them to go to BT.
He said that there's no need to contact them. I simply contact the new provider and they will get in touch with Sky directly to arrange the changeover.
He did ask why I wanted to go. I explained for two reasons:
1) My current connection is intermittant (old and tired router I think)
2) I'm thinking of upgrading to fibre and BT are giving free sports!!
Kept me on hold whilst talking to a manager and then came back to say they are not offering deals on fibre at the moment, but someone from ringback might call me to do a deal. But couldn't guarantee I'd get a ring back.
I think if I order and then cancel, they'll just say, "OK, bye!!"