The absence of diplomatic engagement between Washington and Tehran has exposed a growing gap in the enforcement of international sanctions, with the UK Treasury estimating that up to £300bn in potential illicit financial flows may have gone undetected since the breakdown of nuclear talks in 2022.
A confidential Treasury assessment, seen by this correspondent, warns that the lack of a US-Iran channel has created a vacuum exploited by non-state actors and third-country intermediaries. The document, dated 10 March, notes that the volume of suspicious transactions routed through Dubai and Istanbul has risen by 40 per cent over the past 18 months, with patterns consistent with sanctions evasion on behalf of Iranian entities.
The figure, described by officials as a conservative estimate, encompasses not only direct breaches but also transactions that could not be adequately scrutinised due to the absence of information sharing between US and Iranian financial regulators. Without a formal dialogue, the Treasury argues, the global financial system is operating with a significant blind spot.
The warning comes as the US administration maintains its maximum pressure campaign, a strategy that has yielded limited diplomatic results. Since the collapse of the Joint Comprehensive Plan of Action in 2018, successive US administrations have struggled to construct a sustainable framework for managing the nuclear file and associated sanctions.
British officials have privately expressed frustration at the lack of a coordinated western approach. The Treasury assessment calls for a multi lateral mechanism, possibly under the auspices of the Financial Action Task Force, to close the intelligence gap. It suggests that the UK could play a bridging role given its diplomatic relations with both parties, though such an initiative would require a shift in US policy.
The absence of direct communication has also complicated the return of frozen Iranian assets held in third countries. South Korea and Japan continue to hold approximately £6bn in oil revenues accrued before 2019, with no clear pathway for repatriation. These funds, the Treasury notes, represent a fraction of the broader question over the scale of unmonitored flows.
A Foreign Office spokesperson declined to comment on the specifics of the Treasury assessment but reaffirmed the UK’s commitment to enforcing sanctions rigorously. The US Treasury did not respond to requests for comment.
The implications of the £300bn gap extend beyond financial crime. Analysts argue that the inability to track these flows undermines the credibility of the sanctions regime itself. If sanctions can be evaded at scale, their deterrent effect is diminished, and the diplomatic leverage they are meant to provide is eroded.
For now, the US-Iran impasse shows no signs of thawing. With presidential elections approaching in both countries, the window for a negotiated settlement appears narrow. The Treasury’s warning serves as a reminder that the costs of diplomatic paralysis are measured not only in geopolitical terms but in hard currency.
The figure of £300bn will inevitably be contested. But even if the true number is half that, the revelation represents a systemic failure of enforcement. The question is whether the political will exists to address it.
