I currently subscribe to Sky Sports on Now TV at £25/month plus £3 HD boost.
If I take up BT Big Sport and give my Now TV address, is my subscription and payments to Now TV automatically cancelled?
Or is it safer to use a different address to set up the Now TV part of Big Sport and cancel my existing subscription myself to avoid any possibility of being charged twice?
In my personal opinion, if you have a different email address to use if you do decide to switch, I would roll with that.
You could set everything up from scratch and then cancel the other account.