Hi David,
Try to use ISO from this resource - Download Windows 10 -> https://www.microsoft.com/en-gb/software-downlo...
Instructions:
How to Download Official Windows 10 ISO files Using Media Creation Tool or Directly Using your Web Browser -> https://answers.microsoft.com/en-us/windows/for...
How to Prepare Bootable Install Media for Windows 10 - DVD, USB or SD Card -> https://answers.microsoft.com/en-us/windows/for...
When you will create installation media if you are using antivirus that temporary turn it off.
When issue still persist try to create installation media using different network connection or change DNS settings.
If you have any questions let me know