However, he said they had been advised any further publication of the cables “now knowing they may be a breach of the OSA” could also constitute a criminal offence – to which there was no public interest defence.
“We know these documents and potentially others remain in circulation. We have a duty to prevent as well as detect crime, and the previous statement was intended to alert to the risk of breaching the OSA,” he said.
In a statement, a spokesman for The Mail on Sunday said it was publishing the latest leaked details – despite the threat of prosecution – because “a free press is vital to our democracy”.
“The media must be free to publish such information, in the public interest, as long as it does not endanger lives or national security,” the spokesman said.
“Our readers across the globe now have important information about how Britain tried, but failed, to stop President Trump abandoning the Iran nuclear deal.
“What could be more in the public interest than a better understanding of how this position was reached, which may have serious consequences for world peace?”
In response to the latest leak, a Foreign Office spokesman said: ‘A police inquiry into the totally unacceptable leak of this sensitive material has begun. The perpetrator should face the consequences of their actions.