The expenses investigation facing Maria Miller follows a complaint that she claimed more than £90,000 in second home allowances towards the cost of a house where her parents lived.
The complaint was lodged earlier this week by Labour MP John Mann, who claimed the arrangement was "identical" to that of former Labour minister Tony McNulty.
Mr McNulty was required to pay back more than £13,000 in expenses two years ago, after being found to have effectively "subsidised" his parents from the public purse by allowing them to live rent free in a second home.
Earlier this week Mrs Miller insisted that all of her expenses were "absolutely as they should be" in response to an article in The Daily Telegraph that reported the claims.
These are serious allegations about two special advisers which call their integrity and professionalism into question.
If Craig Oliver threatened the Telegraph without David Cameron’s authority, that looks like an open-and-shut breach of the special advisers' code.
But if the Prime Minister authorised his special adviser to use the threat of Leveson Report discussions to discourage the publication of an embarrassing story, then that is potentially even more serious.
And the same applies to Maria Miller and her special adviser Joanna Hindley – if these allegations are true then one of them has broken the rules.
Downing Street defended its communications director Craig Oliver after he raised the issue of Leveson press reforms in a telephone call to the editor of the Daily Telegraph about a story it was planning to run on the Culture Secretary's expense claims.