Excellent. It's worth looking at the payment details and cancelling the direct debit after the 12th payment has gone through. You should also contact them more than a month before the 12 months is up to say what you are doing. Often they want the contract to last exactly 12 months or to get 30 days notice after the 12 months to cancel. If you do both, there shouldn't be a problem.
If you don't want to, you do not need to tell them who you will be switching to but, depending on the service, you may need a MAC code from Virgin to switch.