The DV FAQ’s on BT website suggest that call divert can only be activated/ deactivated from a DV handset or a ‘regular’ phone plugged into the hub , not from the online BT Control panel .
Its the only secure way, as it confirms that its the end user has set up the divert. If it was done via MyBT, and someone got hold of your login details, then they could divert all of your incoming calls to a number that they own, and security information could fall into the wrong hands, especially as some banks ring with authentication codes. You may not be aware of this for some time.
Just as a final follow up to this, I connected the Smart Hub 2, plugged in a phone and then set up call divert to my BT Mobile using the *21* code and it works perfectly with calls to the landline now being forwarded to my mobile and the call shows up on the landline bill with a zero cost against it.
I've now removed the landline phone and switched back routers and calls still divert so problem solved.
Thanks for the help.
I would still check it works after a week or so, as BT may detect that the line has a "fault", and stop the divert, giving "NU" tone back to the caller. There is normally a separate divert option if the destination number is out-of-service.