Today I went live with Post Office for my phone only and kept my existing AAISP internet provider. I moved both voice and data from BT, with the internet change taking place a couple of months ago. AAISP have been fantastic, their service is LLU. I did however check with the post office about existing broadband suppliers and they assured me that there is no problems keeping current arrangements.
As the whole operation was carried out in the small hours of the morning with no downtime I can safely assume it has not gone TT full LLU.
BT billing however have totally messed up the billing but that's for another post!