We have owed Iran £400 million for almost fifty years. Why? Because we were only to happy to take that money to provide the then Shah with tanks, which could - presumably - be used against his own population that subsequently rose up and deposed him.
Those tanks would then have been used in the Iran Iraq war. Often the Iranian troops would be sent into battle against Saddam Hussein with no weapons. With cardboard cut out guns.
We kept the money. Didn't deliver the goods. We didn't give the Shah his money back - arguably not his money. We didn't give the Iranian people their money back - because we didn't like their system of government. And the feeling was pretty mutual.
If this was any other country they would have access to international court. But its Iran, so they didn't. We could have paid it in humanitarian aid. Could have done something positive instead of - you know - selling tanks and bombs for a living.
We did not.
I don't for a second think Iran was justified for a second in keeping Nazanin Zaghari-Ratcliffe hostage for six years. But it could have been six months or six days or six hours or six minutes or maybe even not at all if we had honoured our actual obligation at any point in the last fifty years.
Boris Johnson in fact as foreign secretary famously made a statement that made it look like there was some justification to Iran's actions. Then shuffled off like the naughty schoolboy he is.
And the fact is, here we are six long years later, paying the debt we legally owed to the country we legally owed it to.
I think we have all learned a valuable lesson here.
If you are an odious oligarch with a bog cash reserve built from the oppression and the blood of your people, Britain is open for business.
But caveat emptor baby