Reported line fault to BT last Friday, I was told that there was a fault but it was outside my property and it would be repaired by today (Wednesday). Arrived home on Friday and found a card left by the engineer to say that they had repaired the fault. I tried my landline and it worked.
I did a speed test on the Uswitch web site and my speed was up to 50Mbps. My BT hub hasn't rebooted itself since and the speed is now up to 57 to 62Mbps. I presume that it may go up a bit more in the next few days as it settles down, hopefully nearer to the 70+ that I should be getting.
Who knows, I may be able to switch to my BT modem and my D-Link DIR-890L AC3200 Tri Band Router.
I'd just like to say thanks to everyone for their advice.
Thank you for posting back. I'm happy to hear that the engineer was able to repair that fault on your line. As long your connection remains stable you should see the speed increase closer to the top end of your estimate. This can take a week or two.