@JohnBurgessUK only! =>
Q: Is it the same computer (not necessarily the same problem) as in this previous thread of yours?
A: It is, but it's completely irrelevant to the question at hand.
Maybe, maybe not.
What's the full name & version of your currently-installed Norton application (e.g., NortonAntiVirus v20.x; Norton 360 21.x; Norton Internet Security 19.x)?
Are you a Time Warner Cable subscriber by any chance?
Does running the following Command, followed by a reboot, resolve the problem?
- ipconfig \flushdns