Tomorrow a very important vote takes place in the European Parliament. MEPs are due to take a decision on whether or not Britain keeps its opt-out from the EU's 48-hour working week.
It could be immensly embarrasing for the Government. Earlier this year, it ended years of opposition to the Agency Workers Directive - which restricts flexible working arrangments in the UK - apparently in return for retaining the opt-out on working time.
But MEPs - in particular Labours' - are now threatening to bulldoze that and vote to end the opt-out. If that happens, then the Government really is in a corner - since the issue will then be voted on in the Council... by a qualified majority.
Apart from the obvious and extremely far-reaching impact of the vote on the economy (as we've quantified today) this is also a classic example of how political agreements and backroom 'deals' in the corridors of Brussels are often not worth the paper they're written on.
As David Yeandle, Head of Employment Policy at the Engineering Employers Federation, told an Open Europe event last week: “With Europe, you think you’ve won, but then you haven’t".
A vote against the retaining of the opt-out tomorrow will send a clear warning to the Irish as they digest the 'political commitments' agreed last week on the Lisbon Treaty: they're not a guarantee - far from it.