Problem solved with replacement Hybrid Connect box. Started a call with BT, on 19th Jan, over another contractual point and mentioned this issue of flashing red bars and was put through to a technical department whose engineers appear to never have heard of this problem. After going through all the troubleshooting steps I had undertaken the engineer conceded the only thing left was to replace the HC which he duly did and it arrived next day.
After connecting it up, initially using Ethernet cable to hub after a couple of minutes the EE logo (no longer BT kogo) went blue as did the bars. I checked the firmware version and it was the same as the prvious HC firmware, so that doesn't look to be the problem. Anyway, then unplugged the Ethernet and moved the HC back upstairs and once started and showing blue bars I disconnected the broadband cable from the router and after a couple of minutes I was onc again connected to the internet via the HC. After a short play I then reconnected the braodband cable and again after a few minutes it looked like service was once again via the homehub. One monir issue was that my laptop didn't seem to want to reconnect with the homehub until after I had rebooted it but other laptops in the house all reconnected automatically.
Interestingly, the negineer conceded that I had been without the EE fallback option since 25th November and was going to arrange a refund for the three months I was without the fallback option. So far this has not materialised but ... 🙂
