Yep, I've run out of suggestions for you...sorry!

Hi ulysses, please take a look at these two fairly recent links which I was looking at yesterday regarding your issue...  I think there may somehow be a connection:

https://community.virginmedia.com/t5/Networking-and-WiFi/Virgin-Media-DNS-not-resolving-domain-names/td-p/5577381

https://community.virginmedia.com/t5/Security-matters/Totally-unable-to-access-Javelin-Trackdays-website-via-virgin/m-p/5577762

Thanks for the links, but they relate to issues in Teeside and I'm in Herts. Also as I said earlier, I have a TP Link router on the same Virgin WAN connection and that's working fine.

But all suggestions gratefully received.

Take the config backup of the router, then factory reset and configure from scratch (basically connect to Virgin only). If that can fix the issue, there must be something in the config...
Again, make sure that the PC is set with static DNS for Primary and Secondary.

If the above does not work, I can suggest the packet capture from the WAN. DrayTek has a guide for that: https://www.draytek.co.uk/support/guides/kb-port-mirror#vigor-2860-2925

He did that about 90 minutes ago...didn't work.

Did you mean Virgin? no idea where you've got Vodafone from...

In an earlier screenshot I see IPv6 enabled (I appreciate this wasn't your router).

If it's on, I would see if everything is the same with it turned off and after a router reboot.