I got a confirmation email from
disconnections@account.virginmedia.co.uk thirty days before my departure date. It all went smoothly from there - on the day of termination I got an email asking me to prepare my V6 boxes and SH4 for collection, which happened a fortnight later. I'd heard horror stories, particularly on VM's own customer Boards, but I can't complain how it worked out for me. Good luck!