The statement from Ofcom is at the very end, and they're very clearly saying you need to only allow moderator-approved on-topic comments on such a blog site in order to fall under the exemption. Any off-topic comment will be subject to the act.

My reading is that as long as the comments are somewhat related, the provider is safe from being held accountable for them, but the exact level of connection isn't clearly defined.

So if you filter out known bad words and spam comments, that could very well cover things.