I'm not disagreeing with you about the requirements for statement of origin on election materiel - that is, as you reference, a matter of fact.
I'm just asking - how can it be election materiel if it is anonymous. The 2 are mutually exclusive since for it to be election materiel it would need to indicate which candidate, party or group the elector is being encouraged to vote for.
To take the stated points in the order they are presented:
Can someone standing to be a parish councillor deliver an anonymous letter - yes, they can, it would appear that they have (by assumption) which would prove that they 'can.'
Can they "tell" somebody how to vote - again, yes they can, they can say whatever they like (within the law) but it doesn't mean anyone has to take any notice.
Does the letter contain "untruths?" It might contain opinions which others disagree with but that may, or may not equate to an untruth. Untruth in politics... Who'd have thought it.
Is it appropriate yes/no?
Does it effect any ones vote?
I'm just testing the theories... Election materiel or just a leaflet about an NDP? If there is a genuine belief that the pre-election guidelines have / are being breached then report it to the electoral registration office for them to adjudicate.