It is expected that MPs will complete their consideration of Clause 1 of the three-clause European Communities (Amendment) Bill sometime between 7pm tonight and 7am tomorrow - at which point the House will start voting on relevant amendments.
But because Michael Morris, the Deputy Speaker who chairs the committee of the whole House, has insisted on playing his cards close to his chest, MPs will not know until this afternoon how many votes there will be. The House could vote for hours.
More importantly, MPs will not know until today whether Mr Morris has acceded to intense cross-party pressure to reverse his ruling that there is to be no vote on amendment 27. The amendment, proposing exclusion of John Major's Social Chapter opt-out from Clause 1, presents the Government with the real prospect of defeat on a substantive issue - although the Attorney General has advised ministers and the House that its passage would not stop ratification.
Because amendment 27 has been debated, it would be most unusual for there to be no vote on it.