Just had an email from BT Sport to say that the price is going up (again!) by £1 from 2nd April. I still have 8 months left in my contract but the email states:
"You don't need to do anything but if you want to change something or leave, and you're within your minimum contract term, you'll need to call us within 30 days of receiving this email to avoid paying a charge for leaving early. You'll need to give us 30 days' notice to leave. We won't charge you for any increase in price during that time."
Meaning you can cancel now without any penalties. Hope this helps someone!