Speaker John Bercow has refused to allow MPs to question the legitimacy of the committee they use to pass judgement on each other - in a move many reformers will view as his worst decision yet from the Speaker's chair.
He's rejected a request from Labour MP John Mann for an urgent question on the floor of the Commons.
Doing so will please the backbenchers who believe their standards and privileges committee works in the interest of MPs and not the public.
But it will enrage those who are deeply disillusioned by senior MPs' ability to set the terms of the punishments they hand down to their colleagues.
By rejecting Mann's call for the issue to be discussed Bercow is propping up the standards and privileges committee - made up of MPs who meet in secret to pass judgement on those of their colleagues who have been found in the wrong.
It's a decision that will leave many reformers shocked - especially after No 10 made it easier for Bercow to allow a bit of public scrutiny in the Commons chamber on the issue.
Whereas yesterday Downing Street was making clear that it backed the existing system of regulation to the hilt, this morning it was confirmed the position is that the prime minister is "very open" to reform.
Yet Bercow, by contrast, isn't even willing to have the matter discussed - despite the scandal of Maria Miller's non-resignation providing a big opportunity to reveal exactly what's wrong with the current system.
The chink in the standards and privileges committee's armour is literally a gap - that between the advice provided by the independent commissioner for standards, Kathryn Hudson, and the decision taken by MPs.
Hudson had said Miller should repay £45,000 in overclaimed expenses - but MPs reduced the amount to just £5,800.
Sir Ian Kennedy, chair of the Independent Parliamentary Standards Authority watchdog set up in the wake of the expenses scandal, has declared the practice of MPs "marking their own homework" has got to end.
Earlier Mann had spoken out:
Public trust in Parliament and in the expenses system has now completely eroded, and we need a new, transparent regulatory system. The standards committee should have its power to rule on MPs’ expenses abolished, and more power should be given to the independent commissioner. We have to stop the practice of MPs regulating themselves.
Yet at noon today Bercow decided to prevent MPs from discussing the issue.
He appears to have made the same mistake as Michael Martin - steadfastly defending the interests of backbenchers when he should have been championing change.
Bercow has a great track record on reforming the Commons. Among the changes is a rehabilitation of the 'urgent question', a piece of procedure which allows MPs to raise topical issues more quickly.
When the government is in trouble they're an excellent device for focusing the Commons' attention to an awkward issue. Bercow is very happy to back parliament over ministers.
When the Commons itself is in the firing line, though, he takes a more defensive view - and not one that is likely to survive the history books.
UPDATE: BERCOW 'OPEN' TO DEBATE
It remains unclear why Bercow chose to decline Mann's request for an urgent question today. But in his response to two points of order from Mann and fellow Labour MP David Winick, he said he was open to a debate on the issue at some stage in the future.
This represents a shift in position - but both Bercow and Downing Street seem to be moving very cautiously indeed.