Problem now resolved. The smart Hub 6 was switched off prior to the smart meter engineer starting the work. He merely switch the main house supply off.
I subsequently tried my old Hub 4, and everything worked first time. All the other devices, voice, and mail functioned normally.
BT engineer for Friday now cancelled and BT are sending me a replacement Hub 6.
You are 100% correct Nigel. The engineer didn't power down the Hub. Merely switched the consumer unit off and removed the main supply fuse.
At a later stage in the day I put my old Hub 4 back in circuit and everything is working properly. BT are kindly sending a new Hub 6 - hopefully by Saturday.
