The vote on whether the inquiry into Libor should be a full-blown judge-led probe or a faster, more limited investigation by Parliament reaches a head in the Commons on Thursday afternoon. A lot has been going on behind the scenes, to try to get a compromise. Labour wants a judge-led inquiry, the Tories don't. Currently there is stalemate.
But the announcement on Thursday morning that Moodys has put Barclays on negative watch is good ammo for George Osborne - he will undoubtedly say this shows that the markets can't wait for a long judge-led inquiry, that there needs to be a swift probe and the lessons put into place quickly.
It puts Labour on the back-foot a bit on the moral arguments, although Labour has always been on a hiding to nothing in terms of the votes in the Commons. Coalition MPs will be whipped and amid no sign of a backbench rebellion the government will, on the face of it, get its way. All Labour can hope for is that it can broker a deal with the government to spread the blame for the mess among both parties.
For Labour any probe is likely to cause reputational damage. After all, they were in charge when the Libor-fixing was going on, it's hard to see how people like Ed Balls would escape from any inquiry scot-free. The political reasons for Labour wanting a long, broad investigation is it raises the prospects of links between the Tories and city financiers being laid bare.
We know many of them have donated to the Conservative Party, these things are impossible to keep secret. Some of these donors have been involved in the sort of casino banking which the government is now trying to insulate from ordinary people's savings.
Labour believes that if it can get an inquiry which will touch on these relationships then at least it won't be the only party in the dock. How often did senior bankers meet Tories, either in opposition or after the last election? Is there any improper reason why George Osborne has watered down the implementation of the Vickers Report, deciding to reduce the amount banks have to hold in reserve?
Although the Tories can win today's vote easily they will have to make clear very quickly who will be sitting on the Parliamentary inquiry. There is the expertise in the Commons and the Lords, but arguably Bob Diamond's appearance before MPs yesterday didn't instil a lot of confidence. Lots of MPs failed to ask the right questions, some of them indulged in political theatre which generated a lot of heat but very little light. MPs might say they found Bob Diamond's evidence "implausible" but it does beg the question - did they do enough to make him cough?
Tories believe that the Parliamentary inquiry being envisaged would be stronger than a normal committee hearing, with legal counsel. But they also face problems over whether any Parliamentary committee can do the job. The City regulator is still probing how widespread the Libor-fixing was, and there is the prospect of the Serious Fraud Office charging people. The problem with previous Parliamentary inquiries into phone hacking was that MPs were unable to draw some conclusions for fear of prejudicing criminal trials.
On Thursday morning it was reported that the former Labour MP Lord McFall might end up chairing the inquiry - the FT reports that he's been approached by the government. This might be a compromise with Labour and would mitigate any claim that the probe would just be a whitewash. The idea of that happening is quite insulting to treasury committee chairman Andrew Tyrie, who asked many of the better questions of Bob Diamond on Thursday.
Ultimately Labour will struggle to maintain the high ground on this - the ominous noises from credit agencies about Barclays present a risk that drawing out this investigation will damage the City of London. If Labour wants to play politics with that, it's taking a serious risk.