Inspired by @Bobson's answer, I would flip it around, to have a law somethig like this:
- Any officer of the Government that provides factual information or responses to any person, in the course of their duties, shall be required to state on each occasion:
a) that the said information may be relied upon;
or, if the reliability of the said information is, or may be, significantly uncertain:
b) Their honest belief and knowledge as to the extent to which it is or is not to be relied upon.
- Failure to explicitly make such statement when communicating factual matters in the course of their duties, other than in the circumstances stated in paragraph 3, shall be a criminal offence.
- A statement referred to in paragraph 2 shall not be required in communications of a transitory nature, unless any party to whom the information is communicated (directly or indirectly) requires the same to be made clear.
That neatly solves it. You effectively impose a duty to state if something is "on the record" (can be relied on), and a right for a third party to require that status to be clarified. You also provide a way to handle uncertainty, or if a member of the public just wants to know where the stairs are (that's a "statement of fact" too).