Jeremy Corbyn, David Davis, Andrew Mitchell & Andy Slaughter

Two weeks ago, we went to Washington to argue for the immediate release of Shaker Aamer, a detainee at Guantánamo Bay. Mr. Aamer’s wife and four children live in London but he has yet to meet his youngest child, Faris, who is now 13.

We are unlikely political bedfellows from the left and right of British politics. The four of us agree on almost nothing, with this exception: Mr. Aamer, a British permanent resident, must be freed and transferred to British soil immediately.

Mr. Aamer was picked up by the Northern Alliance in November 2001 in Afghanistan, where he was doing charity work, and sold for a bounty. He was taken to the notorious Bagram Prison, where he was brutally tortured, before being sent to Guantánamo in February 2002. In 2007, under President George W. Bush’s administration, he was cleared for release. In 2010, under President Obama, he was cleared for release again — after an arduous process requiring unanimous agreement by six agencies, including the Central Intelligence Agency, the Federal Bureau of Investigation and the Departments of State and Defense.

We should never have had to make the trip to Washington. Earlier this year, during his visit to the United States, Prime Minister David Cameron asked Mr. Obama to release Mr. Aamer. The president promised to pursue the matter. On March 17, the House of Commons passed an unusual unanimous motion calling for Mr. Aamer’s immediate release and transfer to Britain. Since that time little, if anything, has been done by the United States.

We heard during our visit that “Congress has prevented transfers”; yet, under current legislation, Mr. Obama could give notice to Congress and then transfer Mr. Aamer 30 days later, as the British government has requested. We heard that there may be “security considerations.” Any suggestion that Britain does not have the legal structures, the security and intelligence skills, or the care capacity to address any issues with Mr. Aamer is deeply insulting.

We are, after all, America’s most trusted ally, and have stood shoulder to shoulder with the United States, expending our blood and treasure, in two controversial wars in Iraq and Afghanistan. Our troops are deployed together in our joint determination to defeat fundamentalist terrorism. Our government, from the prime minister on down, would not press this case with such determination if we believed that Mr. Aamer would put either our allies or our own citizens at risk.

We came to Washington to meet with Obama administration officials and senators to express the British Parliament’s anger that after twice being cleared for transfer, Mr. Aamer is nevertheless facing his 14th year of detention. We were astonished to find a similar degree of incomprehension among the senators we met from both parties. Though we appreciated their concern, their lack of knowledge about Mr. Aamer’s case indicates a troubling failure by the White House to communicate the importance of it.

Our impressions were confirmed during meetings with the president’s special envoys for the closure of Guantánamo. Although almost five months have passed since Mr. Cameron’s request to Mr. Obama, the Defense Department’s special envoy, Paul M. Lewis, and the State Department’s acting special envoy, Charles Trumbull, were unable to adequately answer our questions regarding a timeline for Mr. Aamer’s transfer.

We left feeling shortchanged. If the president has any intention of closing Guantánamo, it will not be accomplished by complaining about Congress, whose members seem to have not been given even basic information about the detainees still held there or about the special case of Mr. Aamer. Mr. Obama must keep others informed — particularly when the omission damages relations with America’s closest partner, as we assured the senators and special envoys that it has.

This is a particularly unforgivable omission in Mr. Aamer’s case because he has never been charged with anything, has been twice cleared for transfer, and is suffering from ill health. Over a decade in Guantánamo would be a long punishment for any crime, if one had actually been committed. Fifteen other British detainees have recently been returned to us and none have been guilty of recidivism. Indeed, while our request for Mr. Aamer’s return has not yet been granted, the American government has seen fit to pay for the transfer of other detainees to Kazakhstan and Uruguay — neither of which has a security or care structure equal to Britain’s. There is simply no reason, domestic or international, for the United States to keep Mr. Aamer in custody.

It is difficult for us to shake off the depressing notion that the Obama administration is indifferent to the repeated requests of the British government. It is a slap in the face for America’s staunchest friend.

These things matter in the war against terrorism. All four of us are senior members of Parliament who represent minority and Muslim communities in our constituencies. The scourge of terrorism will never be defeated unless we can win the hearts and minds of those who might be receptive to the terrorists’ message. And respect for justice and for the rule of law is essential in that battle.