I'm on a 18 month Infinity and calls package and a 12 month BT Vision contract. Will I be contacted before the end of each contract to discuss renewal or will I be auto-contracted for another period if i don't get in touch with BT? Can I keep BT Vision going until the end of the Infinity/calls deal so I can wholesale to another provider.
They might contact you and ask you to sign up for another year. Or they might not.
Most BT contracts do not auto-renew - you should have been specifically told if you signed up for something that does auto-renew. The 18 month and 12 month "contracts" are just the minimum period you agreed to. The contract doesn't end after that period, but you simply go on to paying monthly until you choose to cancel or change the deal.
If you were given a special deal when you signed up, then that will expire and you will pay the standard price for all your services.
If you want, you are free to phone up BT and offer to agree to another 12 months if BT makes it worth your while (you should ask for a discount just like they are offering to new customers). Otherwise, just stick with paying monthly and keep the option of switching to a competitor at a month's notice if you ever want to.