An IP address is "personal data" in the same way that "lifestyle information" or a "location" is. That someone can combine an IP address with other information to personally identify someone is important, but it doesn't prevent me from logging personal data.
The ICO. I've called them up, and they've confirmed their 2011 interpretation of personal data:
https://ico.org.uk/media/for-organisations/documents/1591/pe...
An IP address is "personal data" in the same way that "lifestyle information" or a "location" is. That someone can combine an IP address with other information to personally identify someone is important, but it doesn't prevent me from logging personal data.