THANK YOU, to everybody who contributed to this thread, it has been most helpful and educational. Hopefully for others too who are in the same predicament as I was before this.
FTTP has only very recently been available in this area. The engineer who came to check out my complained about speeds confessed it was quite new to him as previously he had only dealt with FTTC and he only learned some things through talking to a colleague on the phone at my premises.
If I met him again I would suggest that he carries a USB Live UBUNTU stick with him so that he can show the customer that they ARE getting what they paid for and that the limiting factor (after all other checks have been shown to be in order) is their device. He certainly did all the checks he could for my installation.
He may be at a loss as to how to get into the bios on various machines if it isn't already set to boot from USB but worth a try.
I found creating a USB Live UBUNTU stick very simple I imagined it would be quite complicated. I did notice that my 8GB drive now only showed 3.88mb which confused me! But, a bit of Googling showed how to recover the drive back to 8GB Fat32 if I wanted. ( I'm writing this for the benefit of any tyro like me who may be daunted by the process, It IS easy. I followed this guide: https://linuxize.com/post/how-to-create-a-bootable-u... )
At 4AM on my fastest PC I got 1GB Down and 110 Up on UBUNTU via Fast.com Only once, but regularly 980Down.110Up
Happy chappy! Just waiting for the price of GPUs to come down in price so I can build another modern PC.
Once again, many thanks.