Sky retention a will offer you a cracking deal compared to the existing one. Just be prepared to take the line rental with sky. They will be able to offer you something easily £10 cheaper, possibly even free for a period of time.
Regarding contract it will be 12 months, that is standard, but if you do move house you can take the service with you into the new property. Sky have a dedicated house move team & usually they will negotiate a deal when you relocate (usually a new contract again but deal with that at the time). IE they often say we can setup your existing service at your new address if you stay with us for another 12 months.
EDIT you want to speak with cancellations in order to get the good deals. So go through as if you are leaving sky.
Look at overall cost. Sky will be much cheaper to have broadband + phone + line rental, vs having it elsewhere. Their line rental is more expensive but they will be able to discount the broadband price massively if you take line rental so the overall price will be much cheaper.
Also with a home move its sooooo much easier to have one provider who can migrate everything over in one go. It will be one quick call and everything setup, with a date given to you. No contacting anyone else or BT. Sky can do everything and handle it end to end.
Edited by ukhardy07 (Mon 25-Jul-16 22:25:24)