As hard as it is to believe, there was none. Nowhere in the 1,500 pages of materials released under the OIA is anything at all relating to Section 214B being investigated.
No interviews, no legal advice, nothing.
The Electoral Commission wrote to the Police on 10 February 2006. Two weeks later on 27 February 2006 a recommendation not to prosecute is made, justified by just two paragraphs in a report.
I have no idea why the Police did not investigate the Electoral Commission complaint. I can only assume they did not realise the different legal standards in the Electoral Act and reasoned to themselves “Hey we are not prosecuting over S221 so we won’t prosecute over S214B”.