I belive reading Rays helpful post its just the HG612 ( Locked Version) that has the issue.
However Unlocked HG612 are not affected 🙂
Thanks Ray 🙂
Binned the BT modem and HH and replaced with a brand spanking new Draytek 2860. Configured the VDSL settings correctly and bingo everything connected. Now have a stable IPSEC connection (for the last 2 hours!!!) and everything is running as before.
So, looks like the modem firmware issue is still an issue.