Fright night for the government?
A steady trickle of Tory backbenchers are adding their names to the backbench amendment calling for a real-terms cut in the EU's Multiannual Financial Framework for 2014-2020…or budget envelope to you and me.
But for the rebellion to threaten the government's majority, it has to pass the Andrea Leadsom test - in other words, it has to attract most of the pragmatic eurosceptic MPs of the Fresh Start group, which she leads.
And I'm far from sure it will, despite a smart unofficial whipping operation led by the eurosceptic backbencher, Mark Reckless.
Pretty well all Conservative backbenchers, even the few with relatively pro-EU views, believe the EU's call for increased spending is simply potty and completely unjustifiable. But they don't think a British government can single-handedly stop the increase, however much UK ministers stamp their feet.
They think the amendment may be good domestic and internal party politics but is utterly detached from the reality of EU negotiations. Others don't like the idea of voting with Labour, whose recent enthusiasm for cutting the EU budget is regarded on the Conservative benches as rank opportunism. Still others don't want to "cut the legs from under the PM".
If this is to be a "perfect storm" issue, which allows a critical mass of Tory eurosceptics to vote with Labour, then the government has problems. With a number of seats currently vacant, and Sinn Fein discounted, the notional government majority is 85. So, if 43 Tories defy their whips, the government will lose. But only if all the non-Coalition MPs vote with Labour and the rebels. And it is not entirely clear that they will.
I don't know how enthusiastic the smaller parties will be and, crucially, I don't know how hard Labour will whip their troops. They may be quite content to see the headlines about Tory splits - or they may see if they can give the government whips a fright.
And the whips seem to be taking no chances. Strong pressure is being brought to bear on likely rebels, and summonses to meet the chief whip and the PM are being issued. Meanwhile, ministers are cancelling engagements to be present for the vote, and MPs who've been given permission to be absent have been recalled. There's even some talk that the government will declare the vote to be an issue of confidence - which would be quite an escalation.
So how should the result, tomorrow, be judged?
An outright government defeat would be a huge problem for David Cameron, leaving him precious little room for manoeuvre in euro-negotiations - and facing defeat if he fails to deliver a budget cut, and has to try to persuade the Commons to authorise an above-inflation budget settlement.
This result would imply about 60 Tories voting against their whip, and a dangerous loss of confidence in the PM among his troops. This would still be a smaller rebellion than the one over the European Referendum, last October, when 81 Tories defied the whip - almost no-one expects a repeat of that. But it would also be rebellion on a much more substantive issue, in the knowledge that the government would be defeated.
A near-miss, with about 40 rebels would mean the government whips face a permanent challenge, with the potential for real embarrassment over future budget votes. Mopping up efforts, to win back some rebels and marginalise the rest, would continue for quite a while.
A rebellion limited to about 30 Tory backbenchers would be a huge coup for the whips. Compared to the 81 who voted for that EU referendum, it would represent a reassertion of government control and the remaining rebels could be dismissed as a rump of usual suspects, isolated head-bangers and perpetual malcontents. It would deliver a body blow to the credibility of the backbench eurosceptics.
The margins between these results are quite small - handfuls of MPs wavering from one column to another could make all the difference to the way the outcome is perceived. And whatever the result, the ramifications will be more than symbolic.
* And meanwhile in the Lords, an interesting coalition (note the small c) of peers is gathering behind an amendment to the Electoral Registration and Administration Bill (see earlier post). A Labour Peer, Lord Hart, has put down an amendment to postpone the next review of constituency boundaries - and has won support from crossbench peers, Plaid Cymru's Lord Wigley and the Lib Dem Lord Rennard. It's unlikely to be put to a vote at committee stage, but something is brewing.