Gordon Brown has finally won a victory, though it may not have been worth the effort. Nothing much has gone right for him since the late fall, and the most recent polls show Labour almost 20 points behind the Conservatives, and barely ahead of the Liberal Democrats. But the embattled Prime Minister succeeded on Wednesday in pushing through the House of Commons a bill giving the government the right to detain terrorist suspects for 42 days without charge.

The most surprising outcome of the vote was Thursday’s shock resignation from the Commons of David Davis, the Conservative Shadow Home Secretary, and Conservative head David Cameron’s main challenger for the leadership. The Conservatives opposed the 42-day detention law largely because Davis demanded it do so: his resignation, he has announced, is intended to force a national debate on Britain’s creeping illiberality. Davis will now stand for re-election at the by-election his vacancy has created: if he wins, as he seems quite likely to do, his own standing within the Party and his views about British civil liberties will both carry even greater weight.

Of course, the affairs of the Conservatives are no direct concern of Brown’s. But his victory, a narrow nine vote one, came at a heavy cost. The margin of victory will encourage the House of Lords to challenge the bill, which guarantees that the Commons will have to return to it. And that is likely to be an expensive proposition. Wednesday’s vote was won in part by promising the Democratic Unionist Party, the Rev. Ian Paisley’s party, additional money for Northern Ireland, in part by agreeing that those detained and never charged will be eligible for financial compensation–and, in a shameful trade-off, by promising that Britain will support the full resumption of EU trade with Cuba. So, for the sake of a single vote in the Commons, to help win an extra 14 days of detention without charge, on top of the 28 days already granted by the current system, Brown’s government sold the pass on democracy in the Caribbean. This is wrong in principle, bad in practice, and it will lead to entirely unnecessary trouble with the United States.

It is tempting for supporters of a vigorous response at home and abroad to the undoubted dangers of Islamic terrorism to defend the proposed law as a disagreeable necessity. And since the US–correctly–claims the right to make its laws without being subject to European carping, it ill-suits Americans to be too hard on other democracies that demand the same privilege. But the government throughout offered no defense of the 42 day measure, except to claim that it might at some point in the future be necessary. That is a slender basis on which to base such a far-reaching claim for increased state power, which is why the Tories voted against it. And, frankly, 42 days is a lot, far more than is allowed in the U.S., and somewhat more even than in most continental states. One wonders if terrorists in Britain are so much cleverer than their counterparts elsewhere, or if Brown’s bill is mostly a tacit admission that the British security services are, as they have hinted, in danger of being swamped by Islamists.

The only thing that makes me sympathize with Brown is that he is at least advancing a measure–supported, one might add, by the majority of the British people–that takes the Islamist threat seriously. It has been passed at too high a price, and it has been defended with arguments that do not command respect. But too many of its opponents–though not Cameron?s Conservative Party–belong to that disreputable school of civil libertarians who, while petrified of their own government, are insouciant about the dangers Britain and the West faces–indeed, they blame their government for creating what they deny is a problem. Brown may have won the vote on Wednesday, but it is Cameron and the Tories who, with their measured opposition, have won the argument.