I have just sent this reply to the BG email.
"Hello,
Thank you for your email.
From the Ofgem website:
What happens if your energy supplier goes bust
When your new supplier contacts you
Ask your new supplier to put you on their cheapest tariff,
or shop around and switch if you want to. You won’t be charged exit fees. Your new supplier will explain how they'll manage your account balance, including any credit refunds.
I have shopped around and found the provider I prefer. However, my preferred provider informs me that you have blocked the switch.
I would be grateful if you could remove the block and allow my chosen provider to take over the supply.
Kinds regards,"
Let's see if they follow Ofgem's guidelines.