The week before last, 81 Conservative MPs ignored the blandishments of the party whips, and the pleas of Prime Minister David Cameron, to demand a referendum on EU membership.
It was the biggest rebellion of Mr Cameron's six years as party leader, but with Labour also supporting the government, it was far from being the tightest parliamentary vote since the Coalition took power.
For that, you would have to go back to July, and the vote on whether the government should contribute an additional £9bn to the International Monetary Fund to help prop up other countries’ ailing, debt-ridden economies.
On that occasion, the Coalition's majority was reduced to just 28 votes, with 32 Tories joining Labour in the lobbies to oppose the bailout plan.
At the time, Chancellor George Osborne hoped that would be the end of it, and that the international debt crisis would be making no further claims on the generosity of British taxpayers.
But in the wake of the Eurozone crisis, and specifically the Greek bailout, it seems that yet more billions will be required after all.
Mr Cameron was at great pains to stress yesterday that increasing Britain’s contributions to the IMF does not mean UK taxpayers are propping up the Euro.
“Britain will not invest in the IMF so the IMF can invest in a Eurozone bailout fund. That is not going to happen,” he said.
But nevertheless, there is a certain amount of hair-splitting, if not to say outright disingenuousness, going on here.
The role of the IMF is after all to help countries in economic distress all round the world – and there seems no reason why that could not include countries in the Eurozone.
Shadow Chancellor Ed Balls has called on the government to make clear that “directly or indirectly this money will not end up supplanting the European Central Bank and putting liquidity support in for Spain and Italy. “
As the mischievous Mr Balls knows perfectly well, there are plenty of Tory backbenchers who privately suspect this is exactly what is going to happen to the additional IMF cash.
So why is this such a potentially difficult issue for Mr Cameron? Well, do the maths.
If there was a rebellion on the latest IMF handout, only this time on the scale of the EU referendum revolt, the government would not only lose – but lose big.
It is clear that Downing Street has already wised-up to this danger and is trying to argue that a second Commons vote would be unnecessary.
Asked about it yesterday, Mr Cameron said the July vote had "allowed for some extra headroom and what we would anticipate doing would be within that headroom.”
And there is, of course, another reason why the government is keen to avoid such a vote – namely that it would further highlight the divisions in the Coalition between his party and the Liberal Democrats.
The Coalition’s inherent instability derives from the fact that it is a marriage of convenience between two parties with wildly differing worldviews, and on no single issue is this more clearly exemplified than on that of Europe.
The Lib Dems, at some cost in terms of their own popularity, have consistently advocated the concepts of European integration and “ever closer union” for most of the past 30 years.
By contrast, the Tories have been drifting steadily in the opposite direction – to the point where Mr Cameron – our most Eurosceptic premier since we joined the EU – is seen by some on the right of his party as a creature of Brussels.
Going into this year, it seemed likely that electoral reform would be the rock on which this fragile Coalition ultimately foundered, but already that seems a very distant memory.
While the debacle that was the AV referendum in May has effectively buried that issue for a decade, the issue of Europe has risen phoenix-like from the flames.
Mr Cameron spent a good part of his leadership in the early years telling his MPs to stop ‘banging on’ about Europe, doubtless conscious of the fact that the issue had destroyed the last two Conservative governments.
Now that it is back on the agenda, I suspect they won’t stop banging on about it until it has broken this one too.