Thank you all for your help in this matter.
As suggested, I have connected my MS Surface laptop via a USB3 adapter to the router by way of a CAT6 cable and tried both Okla and SamKnows spped tests at various times.
3 interesting facts, the first being that the difference between the two speed test facilitators was less than 10% on all tests.
The second is that the difference between hard wired and WiFi using the laptop locally to the router was circa 15% to 20%
and finally the third... on all tests attempted, the maximum download was less than 90Mb
So as a final proving trial to ensure it is not my equipment, I took my laptop etc to my sons house who also has Virgin but the 200Mb service and is in the same area as me. The results were both astonishing and annoying in equal measures... I averaged during the tests in excess of 200Mb by hard connection and just over 160Mb by WiFi.
And I pay for a 350Mb service and get less than 100Mb on a best day but usually closer to 40Mb. I am keeping records of all the testing that I have and continue to do.
With regard to the apparent testing of my service and reuslting in no problems found, perhaps a check of your equipment for accuracy is in order?