To read Richard Ratcliffe’s long investigative article about the purported reasons behind his wife’s situation, one can sense the burning sense of injustice and betrayal he feels.

Not only has his wife been arbitrarily and unlawfully kept as prisoner, for years, by one of the world’s most capricious systems of hostage-taking — by a nominally legitimate state — he has also suffered the dual humiliation of being strung along by two governments: Iran’s, and ours.

The foreign secretary said last week that the treatment Nazanin Zaghari-Ratcliffe has suffered in Iran “amounts to torture”. He is right. Years of detention for no reason is an act intended to humiliate and hurt. It means suffering. And with each iteration in what Zaghari-Ratcliffe has suffered, each new return to prison after a mirage of freedom or relaxation, the torturer emerges from the judge, the jailor, and the bureaucrat.

Richard Ratcliffe alludes to other forms of torture in his piece.

Raab is right that this is torture. Why, then, does his government not act as though it is? Richard Ratcliffe believes that Britain has been passive in Nazanin’s case because she is an easy target: someone individually unimportant, a dual national, just forgettable enough for the government to push to one side.

But the story of the past six years is also in large part composed of Britain’s increasingly desperate efforts to remain on Iran’s good side. This, despite everything Iran has said and done — not only to Britons and British interests, but to its neighbours, and its own citizens.

Britain is an eager member of the P5+1 group — the permanent members of the United Nations Security Council plus Germany — which has fought to keep the essential framework of the Iranian nuclear deal in operation. Even after it was abandoned by America and Iran — and Iran began once more publicly enriching uranium, and boasting about its development and use of ballistic missiles.

Unlike the United States, Britain has never bowed from its stated desire to trade more with Iran and to accept Iran’s government as it stands. These commercial and political relationships trump any concerns Britain either feels or expresses about Iran’s numerous expeditionary wars abroad; its gunning down of protestors in neighbouring countries; its acts of international economic terrorism against Saudi Arabia and even Britain; its posturing threat to close now-open sea lanes; and, indeed, Iran’s continual taking of hostages from Britain and other allied countries.

None of these things cause Britain to doubt its engagement with Iran, or eagerness to conclude whatever deal proves eventually acceptable to the Americans.

For Richard Ratcliffe’s part, one can see the absurdity in all of this. Britain is willing to excuse Iran so much — and yet the nominal reasons for his wife’s imprisonment have proven intractable.

The Iranian nuclear deal involved the unfreezing of billions of dollars of Iranian assets, something which is continually raised by Iran in relation to the hostages it takes. In the deal’s most visible and infamous moment, the Americans airlifted first millions, then billions, of dollars of unfrozen Iranian cash into Iran proper.

But Iran wants more money, and faster, than has currently come its way. And it justifies all its hostile actions in relation to specific sums and niggling debits — which its leaders know can be pursued more easily through imprisoning those vulnerable to kidnapping than through any system of international arbitration.

Many of these assets were seized entirely legitimately, and for good reason. Some were taken from Iran in 1979, after the shah was overthrown and Iran became a newly militant state, pledging to begin a violent theocratic overthrow of the world order. Other seizures followed specific outrages linked to Iran, for example the 1983 Beirut barracks bombings which murdered hundreds of international peacekeepers in Lebanon.

The debt for which Nazanin Zaghari-Ratcliffe is held is of the former type. The shah had paid in advance for British-built tanks, which, after the revolution, Britain did not want to hand to an expansionist theocracy. Britain kept the tanks and the money, now estimated — following decades of court cases, to be around $400 million. Ratcliffe is certain that this debt is the sole reason his wife is dragged unwillingly between court and prison, for years on end.

Britain’s government has gone to idiosyncratic lengths to keep hold of this money when otherwise it is relaxed about Iranian military development and indeed, enriching Iran. It has privileged a company, International Military Services (IMS), which is wholly owned by the state, in the process.

Recently rumours have gathered that Britain was about to pay roughly $400 million to Iran in exchange for some hostages. Richard Ratcliffe alludes to one other currently held by Iran’s Islamic Revolutionary Guards. The Foreign Office has thoroughly denied these suggestions.

Whatever ends up happening, the process has shown the bizarre lengths to which countries must now go to deal with Iran. The Iran deal which was concluded last decade did not stop Iranian wars across the Middle East, and nor has the gradual unfreezing of assets afforded anything but more insistent demands from a taker of hostages.

With Britain painfully ambivalent on all of these questions, one wonders why the payment of one particular debt has created so many years of trouble. A less passive government could keep the money and justify doing so — but one as weak and equivocal as ours struggles even to do the same.

All of which draws into question why Britain remains bound by a non-functioning Iran deal framework if it forces the country to liberate millions of pounds to an open aggressor, or keep suffering the individual torture and collective humiliation of Iran’s hostage diplomacy.