Last November I obtained a MAC code from Virgin (ADSL) and tried to migrate to BT. BT initially told me that the MAC code from Virgin was invalid, so I called Virgin and obtained a new one over the phone. With that, BT successfully completed the migration and started providing my phone and broadband services.
Virgin have not stopped taking money from me by Direct Debit each month. I called to query this and they deny ever having issued the second, valid MAC code. This is due to their policy against keeping records of phone conversations - I learnt my lesson and now only communicate by ema