After coping with the low speed for a couple of months, I was resigned to the fact that the ethernet port was not operating at full speed. However a failure of my SSD resulted in having to re-install Windows 10 on a new SSD. After activation, on checking the speed I got 380 Mb/sec. This leads me to believe that the problem lay with a Windows update on a system which had been updated from Windows 8. The only changes to the system are a new SSD and a new installation of Windows 10 1903. I am not suggesting that Windows was at fault but it would have been too much of a coincidence if a Virgin Network fault had been corrected at the same time.