In an unprecedented public speech, John Sawers, the head of MI6, said that intelligence activities were responsible for Iran's admission last year of a second enrichment plant, which in turn led to tougher diplomatic pressure.
"Stopping nuclear proliferation cannot be addressed purely by conventional diplomacy. We need intelligence-led operations to make it more difficult for countries like Iran to develop nuclear weapons," he said.
Mr Sawers's comments come as six world powers seek to resume talks with Iran over its nuclear programme, which Tehran insists is for civilian purposes but which Western powers suspect is intended to develop atomic weapons.
The UN Security Council voted for fresh sanctions against Iran in June, the fourth set since December 2006 over its nuclear programme.
"The revelations around Iran's secret enrichment site at Qom were an intelligence success. They led to diplomatic pressure on Iran intensifying, with tougher UN and EU sanctions, which are beginning to bite," Mr Sawers said.
"The Iranian regime must think hard about where its best interests lie."
He added: "The risks of failure in this area are grim. And the longer international efforts delay Iran's acquisition of nuclear weapons technology, the more time we create for a political solution to be found."
Iran notified the UN nuclear watchdog in September last year that it was building a second enrichment plant near the central city of Qom, after Washington accused it of covertly evading its responsibilities under the Non-Proliferation Treaty.
Mr Sawers's speech was the first public address by a head of the Secret Intelligence Service (SIS), as MI6 is officially known, and marked his first year in the role.
Zayed Sustainability Prize
The smuggler
Eldarir had arrived at JFK in January 2020 with three suitcases, containing goods he valued at $300, when he was directed to a search area.
Officers found 41 gold artefacts among the bags, including amulets from a funerary set which prepared the deceased for the afterlife.
Also found was a cartouche of a Ptolemaic king on a relief that was originally part of a royal building or temple.
The largest single group of items found in Eldarir’s cases were 400 shabtis, or figurines.
Khouli conviction
Khouli smuggled items into the US by making false declarations to customs about the country of origin and value of the items.
According to Immigration and Customs Enforcement, he provided “false provenances which stated that [two] Egyptian antiquities were part of a collection assembled by Khouli's father in Israel in the 1960s” when in fact “Khouli acquired the Egyptian antiquities from other dealers”.
He was sentenced to one year of probation, six months of home confinement and 200 hours of community service in 2012 after admitting buying and smuggling Egyptian antiquities, including coffins, funerary boats and limestone figures.
For sale
A number of other items said to come from the collection of Ezeldeen Taha Eldarir are currently or recently for sale.
Their provenance is described in near identical terms as the British Museum shabti: bought from Salahaddin Sirmali, "authenticated and appraised" by Hossen Rashed, then imported to the US in 1948.
- An Egyptian Mummy mask dating from 700BC-30BC, is on offer for £11,807 ($15,275) online by a seller in Mexico
- A coffin lid dating back to 664BC-332BC was offered for sale by a Colorado-based art dealer, with a starting price of $65,000
- A shabti that was on sale through a Chicago-based coin dealer, dating from 1567BC-1085BC, is up for $1,950