Received resolution letter from Plusnet today and they offered £30 goodwill gesture. Which is really fair and I have accepted graciously as full and final resolution.
And for fairness the Complaints team at Plusnet were great throughout - I had a personal contact who I could phone and they always backed up with an email to let me know an alternative contact when they were out of the office. So fair play to Plusnet.
Origin less so at the moment