InstallerUFB: The other thing to consider - Is that as you have altered the power wireing (by installing another cable (in the same set of holes) your house wireing is no longer code complient therefore voiding your house insurance should there be any issue caused by this wireing
No not true, the home owner is able to this, they may replace, and even move socket outlets ( and therefore fixed wiring) they may not extend a circuit ( add fixed wiring).
There are no legal problems running the cat 6 down an existing hole with 230v however you may not run the 230 at the same time or after the cat6
Yes I know this is stupid but that is the way the law is written.
As for the code of compliance, that has no effect except at the time the house is signed off. Anyway the extra low voltage wiring does not form part of the document. Any alterations to a house that do not require consent ( eg network cabling) do not require any sign off by anybody. Insurance is not an issue.