Earlier quoted context omitted.
However, is it not thought that because the ISP keeps a log of dynamic IP addresses, these could (in theory) be matched to the IP address of anonymous comments, thus de-anonymise them?
No, because you need to take into account the effort needed to de-anonymise the IP address. > > (26) The principles of data protection should apply to any information concerning an identified or identifiable natural person. Personal data which have undergone pseudonymisation, which could be attributed to a natural person by the use of additional information should be considered to be information on an identifiable na…
IANAL, but I'd be wary of saying that you'll be fine storing dynamic IP addresses. You'll probably need to have a rationale as to why you don't consider it.