Thanks for the replies. Microsoft support advised me today (they don't work weekends) to manually set a DNS address in my network settings, rather than automatically obtain. This is apparently their fix to this issue, and they were even able to give the DNS server address for my ISP, so I guess they've done this a few times now.... That's fine for my home PC (and it is now working properly), but I am not sure the laptop will be okay the next time I log in to someone else's network with a different ISP. Will have to wait and see...
I'm not a technician but changing the way Windows does this seems like a strange thing to do. I've never heard of this with any other operating system.