The summoning of the Iranian ambassador to the British Foreign Office on Wednesday over broken assurances about the destination of an Iranian oil tanker, and now the arrest of two British-Australian nationals, marks yet another stage in the mutual blame game between Britain and Iran that leaves the relationship stuck deeper in a frustrating rut.

From the British perspective, well articulated by the former Middle East minister Alistair Burt, those in the UK government who would have liked to build a new relationship with Iran in the wake of the 2015 nuclear deal feel very badly let down by Tehran.

Not only has there been no progress in high-profile consular cases such as that of Nazanin Zaghari-Ratcliffe, arrested for spying in 2016, there has also been a steady stream of other British-Iranian dual nationals picked up on spurious grounds in recent weeks. Kameel Ahmady, an Iranian-British social anthropologist was arrested on 11 August and had no contact with his family except three phone calls. On 27 August, another Iranian-British citizen Anousheh Ashouri, a businessman who has been imprisoned since 2017, had been sentenced to 12 years in prison allegedly for spying for Israel’s Mossad intelligence agency and receiving €33,000 (£29,000) in illicit funds.

On 18 August, Iran’s appeals court upheld a 10-year prison sentence against British Council employee Aras Amiri for “forming and organising a network for the purpose of overthrowing the Islamic Republic.”

The latest arrest of three Australians, two with British passports, came around this time, but marks a new low point since they had no Iranian nationality. It has even led the Foreign Office to discreetly warn UK journalists thinking of travelling to Tehran independently against doing so.

There is a general crackdown on free speech under way in Iran, covering Iranian journalists and human rights activists largely ordered by the judiciary chief Ebrahim Raisi, appointed in March 2019. The arrests have been the subject of public protest by reformist MPs.

But there is no doubt in British minds that these Australians have been targeted because of the approach of the UK and Australian governments to the wider Iran crisis.

Similarly there is real anger in the Foreign Office that Iran has broken assurances given to British and Gibraltarian officials on what is said to be five occasions that if the Iranian ship seized by the British was released, it would not travel to Syria to unload its oil. Those assurances were given in a note, as well as verbally and personally by the Iranian foreign minister, Javad Zarif, British diplomats say.

Iran’s envoy to London said on Wednesday the oil cargo of tanker Adrian Darya 1 was sold at sea to a private company, denying Tehran had broken assurances it had given over the vessel. He also insisted any EU’s sanctions on exports to Syria did not apply to Tehran.

The original impounding of the ship by the British on grounds that it was intent on breaching the EU embargo on oil sales to Syria, may not have been a far-seeing piece of UK diplomacy, and largely reflected US private pressure to do so, but the ship’s release was negotiated by the British in a matter of five weeks.

It was also released on 15 August in the knowledge that Iran had not yet released the British flagged Stena Impero, which was seized on 19 July as it passed through the strait of Hormuz. Seven of the 23 crew have been released, but the ship remains in Iranian hands.

The Iranian Foreign Office at the weekend said the ship would be released soon, but in the complex Iranian government, the writ of the Iranian Foreign Office is not sacrosanct.

From the British perspective the episode has made the UK look naive in the eyes of the US administration for even taking the Iranians’ words seriously. The now departed US national security adviser John Bolton openly mocked the British for being in denial about the true nature of Iran.

British advocates of dialogue, such as Burt, say Tehran does not seem to understand the value of a unilateral gesture on issues such as releasing hostages, or how it could unlock something different.

From the Iranian perspective, the catalogue of British failings is equally long. Grace 1, the Iranian ship, should never have been impounded since Iran is not obliged to follow an EU sanctions regime. The UK government has spent close on 30 years, and millions in legal costs, in refusing to pay the debt courts say it owes to Iran for the sale of Chieftain tanks.

Above all Europeans, including Britain, talk a big game about the need for European sovereignty, but faced with an overweening US administration imposing sanctions on anyone that trades with Iran, the EU has proved powerless, and says the effectiveness of such sanctions is a necessary by-product of the dollar’s ubiquity as a trading currency.

The bigger question is whether the departure of Bolton will, as hoped, reveal an opening in the cul-de-sac that is western-European relations. Burt, speaking to the Lords international relations committee last week, made the point that if Trump has decided not to go to war with Iran, as he appeared to when he did not retaliate for the downing of a US drone by Iran, the logical step must be to talk Tehran.

Emmanuel Macron, the French president, has been trying to create the detailed circumstances for this to occur. The US administration said again that Trump was willing to hold a summit with the Iranian president, Hassan Rouhani, at the UN general assembly in New York this month.

But for these high-profile “look me in the eye” summits to work, or for there to be any relenting on US sanctions, the ground debris has to be cleared. Issues like impounded ships, broken promises and hostage-taking have to be addressed. At the moment, there is no sign that is happening. If anything the thicket of disagreements is only becoming more dense.