Thanks for your post and welcome to the forums. It's great having you on board with us in the Community.
It all depends on the context on this one.
All contracts are minimum term ones meaning that once the minimum term is over they revert to rolling monthly contracts as mentioned above. In this example, no permission would be needed since this is agreed at the start.
If you are referring to contracts that last for 12 months and then a new 12 month one is taken then yes - we would need permission to do this. Your usage of the service after any changes would class as acceptance. We would send you a new contract via post or email though.
If you have any specific questions, come back and let me know.