LONDON — Since the “war on terror” began, various policies have been adopted on both sides of the Atlantic that have played on, or exacerbated, our fear of the “Islamic extremist.” Perhaps none has been more pernicious than the recent British practice of stripping citizenship from dozens of people who were considered possible terrorism suspects, as soon as they traveled abroad — which then made it less politically complicated for American agents to hunt them down as dangers.

The power to strip dual citizens of their British rights — habeas corpus and the presumption of innocence included — has been on the books here for decades, but had not often been used until 9/11. Since then, 42 Britons have seen their passports torn up by the home secretary; of these, 40 have been Muslims. Even more troubling, at least some of these people were clearly singled out because the United States had designs on their lives or their liberty. Two Britons who lost their citizenship were killed later in American drone strikes. Another was kidnapped and rendered to the United States.

Last Monday, the House of Lords defeated an effort by the government to go even further — to expand its citizenship-stripping powers to include people who held only British citizenship, a step that could render them not just more vulnerable but also stateless. We can admire the respect that Parliament’s upper chamber showed for the rule of law, but it is small comfort: In January that bill sailed through the House of Commons with only 34 votes in dissent, and now a committee of the two houses will decide what comes next. Clearly, with the London bombings of 2005 in mind, the Commons is still acting on fears that Muslims who might be radicalized abroad will return home to threaten the British Isles. Until those fears recede, we can expect continued maneuvers to quicken our retreat from traditional standards of British justice.

Something similar is being hinted at across the Atlantic; we see suggestions on America’s far-right fringe that dual citizens who fight alongside jihadis in Syria should lose their United States citizenship. But Americans, at least, have limits that prohibit making anyone stateless. In 1958, the Supreme Court decided Trop v. Dulles, a case that clarified the Eighth Amendment’s proscription against “cruel and unusual punishment.” The court was asked whether it was constitutional to deprive people of their citizenship when doing so would leave them stateless. It answered that statelessness was “a form of punishment more primitive than torture.”