The No Fly List is not a government program easily challenged. Indeed, it operates in secrecy, from an undisclosed location, administered by an office – the Terrorist Screening Center – that doesn’t accept public inquiries. When challenged in court, the watchlisters routinely declare their methods safe but secret and fight the disclosure of their standards and criteria for inclusion.

The British Muslim family recently denied travel to Disneyland might soon discover this, despite the fact that Prime Minister David Cameron has been called upon to examine the case.

The Guardian reported that, despite prior US approvals, the entire family was turned away from Gatwick’s departure lounge. Without warning or a hearing, their freedom to travel was stripped away at great expense and deep humiliation. Instantly, they were reduced to the status of suspected terrorists by anonymous US officials working without any judicial oversight.

Imagine your family in their shoes. If you can’t, then you don’t understand the power of the US No Fly List.

Just ask Ayman Latif, an honorably discharged US marine who sought to return home from abroad to shore up his veteran’s benefits. Without any offered reason or warning, he was exiled by a system that he has spent the last five years challenging in federal court.

Or ask Rahinah Ibrahim, now a distinguished architect and scholar. As a Stanford University graduate student she found herself arrested and handcuffed in front of her young daughter when she sought to travel from San Francisco to an academic conference. Her eight years of litigation finally uncovered that an FBI agent had mistakenly watchlisted her; the presiding judge labeled it “a bureaucratic analogy to a surgeon amputating the wrong digit”. (Full disclosure: I testified on behalf of Dr Ibrahim at the first and only such trial held so far.)

Or ask many others (whose stories are told in my book on the subject) who say they found themselves at the tender mercies of government officials – typically FBI agents – offering their help to get off the list in exchange for becoming government informants when they returned home.

It’s not just Muslim names on this sad list. Although accusations of racial profiling have haunted the use of the No Fly List in the past, for every Mohammad Tariq Mahmood (one of the Gatwick 11), there is a Cat Stevens or Ted Kennedy or John Lewis.

In this story, however, lies a cautionary tale for travelers regardless of citizenship or religion.

Thanks to some courageous lawyering in tough, often pro bono cases, startling information has been pried from officials: the standard for inclusion on this list is often based on a “predictive judgment”, a “reasonable suspicion” that someone is a “suspected terrorist” presenting some sort of future threat.

“In other words”, one federal judge wrote, clearly dismayed by the departure from traditional legal requirements that someone be guilty of some action before deprived of their rights, “an American citizen can find himself labeled a suspected terrorist because of a ‘reasonable suspicion’ based on a ‘reasonable suspicion’.”

Indeed, the cautionary tale grows grimmer still. For there is no logical reason why terrorist watchlists need be limited to air travel. Indeed, few realize how many watchlists already exist until they find themselves in their crushing grip. There is, of course, a watchlist for maritime travel. And this month President Obama urged the use of the No Fly List to deny access to firearms.

Whatever one’s views of the second amendment to the constitution, the evidence is unmistakable. A list once confined to stopping hijackers and 9/11 style bombers has grown into the go-to tool for government officials who don’t like their predictive judgments questioned by lawyers and judges.

Slowly, federal lawsuits have forced some light on to this system and forced back the worst abuses. But there is still a long way to go. Whatever US officials suspect of this British family, they deserve respect for the fundamental right we all must protect at our peril: equal justice before a neutral magistrate in a public forum.