CeeGee: So, having called Snap and had them take me through basic set up, decided the modem was fine and to log a fault with Chorus. Chorus of course were rather busy as it wasn't just me with a problem several calls and three days later, with Chorus working their way down the fault line to my door, they fix several things and then confirm the box Snap said was fine was cooked.
So, replacement non Snap box & things are back up and running. And no, Snap cannot sell me a new box thanks - won't buy off someone who insisted the old one was working when it was not. They need to know the limits of their ability to remote diagnose.
Thanks for the suggestions here team, as always its nice to know people are willing to share their expertise and experience
so you tried a new modem and it worked?
is your fritz under contract still? likely snap will happily replace it for you.
Snap are official distributors for fritzboxes, and do outright sell fritzs if you ask in the right places.