By Tom Bradby: ITV News Political Editor

The news that we are re-opening our embassy in Tehran is a startling development in a remarkable week.

It represents a striking potential turnaround in our dealings with Iran, which have by and large been marked by extreme hostility for a generation.

In fact, one might say for much longer than that. There are plenty of people who have reasons to resent us, but few more so than the Iranians.

If you are unfamiliar with the history of the region, you won't perhaps be surprised to learn that our relationship with the country has its origins in our urgent search for one commodity; oil. Iran had a great deal of it and we wanted it.

So, through the auspices of the Anglo-Iranian oil company, we developed and extracted vast quantities of black gold, which helped keep the Imperial Fleet on the high seas but made very few Iranians any richer.

In fact, plenty of historians would argue that the story of the British Empire would have been very different without Iranian Oil.

Protesters in Tehran topple the British emblem on the embassy building in 2011. Credit: Parspix/ABACA/PA

The British Foreign Office and MI6 generally ran the internal affairs of Iran with one purpose in mind; to keep the oil flowing.

However, after the Second World War, there was an upsurge in nationalism in Iran, as there was in so many other countries and the Shah we had installed on the throne in place of his father felt he had no choice but to appoint a Gandhi-like figure - Mohammad Mosaddegh - as his Prime Minister.

Mosaddegh wanted a better deal for the Iranians for their oil. We told him he couldn't have it. He went to the UN and begged and pleaded.

Eventually, he lost patience and nationalised the Anglo-Iranian oil company. We called him a communist and said he was working in league with the Soviets (which he wasn't).

This was the first time the British Embassy in Tehran was closed.

The Anglo-Iranian oil refinery, the worlds largest, at Abadan, Persia, Iran in 1951. Credit: PA Archive

The Americans didn't like Mosaddegh any more than we did and in 1953, the CIA, with help from MI6 and its many long standing contacts in Tehran, staged a coup to get rid of Mosaddegh.

The officer who arranged it was so pleased with the way he bribed crowds and officials that he wrote a book called 'Countercoup', which ended up as something of a training manual for all future such coups, like those in Saigon and Santiago and many other places besides.

The net result was to give absolute power to the Shah who remained a staunch ally of both the British and the US right up until 1979.

Our embassy re-opened. The oil started flowing. The Shah and his cronies got very rich and bought lots of armaments, not to mention plenty of fast cars.

The trouble was that lots of Iranians hated him and his repressive security forces.

The only place that anger could be channeled was into the mosques, which is why the revolution against him, when it exploded, was partially religious in nature (the mullahs hated many of his more liberal reforms, some of which we in the West approved of).

So we ended up facing a theocratic regime in Iran that disliked Western influence in general and Britain and America in particular (because of our opposition to Mosaddegh and support for the Shah).

You might say this fact has underscored Western policy in the Middle East ever since. The principle reason we supported Saddam, for example, was because he was supposed to be a bulwark against the Iranians.

Former Iraqi President Saddam Hussein Credit: Furst David/ABACA/PA

This hostility persisted up until last week. We have been on totally different sides in Syria, the British and the US supporting (periodically) the rebels, whilst the Iranians have devoted considerable energy and resources to propping up the Assad regime.

And yet now we have both Iranian and probably American and British Special Forces more or less in next door buildings to each other in Baghdad as they face a common - and frightening - enemy in Isis.

John Kerry may have been slapped down for talking about the possibility of military co-operation with the Iranians, but most of us suspect that is what is already happening on the ground.

The Americans and Iranians certainly aren't going to want to bomb each other by mistake.

So what does it all mean?

Well, not instant rapprochement, that is for sure. Our intelligence establishment has welcomed the slightly more outward looking style and rhetoric of President Rouhani ever since he was elected in Tehran, but they also say that the Supreme Leader - who still holds the reins of power - is running a 'twin track' foreign policy, with one strand in the hands of Rouhani and the other in those of the leaders of the Revolutionary Guards (who have been in charge of policy in Syria).

Is this the moment where there is a genuine sea change?

Well, perhaps. It is certainly an intriguing moment.

Intelligence agents I have spoken to are talking about the possibility that, in reality, Iraq has already been broken up.

So the map of the Middle East is being redrawn before our eyes.

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