Mr Cameron, having yet again to defend publicly his Cabinet colleague, let it be known he was now "very open" to tougher regulation of MPs.
Having refused a Labour MP's application to call a Coalition minister to the Commons to defend Ms Miller, Speaker John Bercow, in response to points of order from Opposition backbenchers, said MPs' concerns about self-regulation were "widely shared by our constituents" and he made clear he was "very open" to the idea of a debate on the subject.
After looking into her expenses, Kathryn Hudson, Westminster's standards watchdog, ruled the Culture Secretary should repay £45,800. Yet the Commons Committee on Standards, which has the final say on issues of ethics and discipline, reduced this to just £5800.
Documents showed Ms Miller told Ms Hudson she might go over her head to ask MPs to intervene. There have also been claims of intimidation, since denied, that pressure was put on newspapers to stop probing into Ms Miller's expenses.
The Culture Secretary was cleared of funding a home for her parents at taxpayers' expense but was criticised by MPs for taking an obstructive attitude towards the standards commissioner's inquiry.
One senior Tory demanded the PM sack Ms Miller and accused him of "scrabbling around for a line to take to avoid having to confront her".
Another described the situation as "ghastly", noting: "It is just making us look all the same. "
But Mr Cameron has stood by his colleague, saying yesterday: "What matters is doing the right thing. Maria has done the right thing by repaying the money, making an apology and now getting on with her job."
Pressed on whether she was still in her post because she was a state-educated woman, the PM replied: "Maria Miller is in her job because she is doing a good job as Culture Secretary."