British police launched an investigation into the leak of diplomatic correspondence of the UK Ambassador to the US Kim Derrota, which contained criticism of US President Donald trump and his administration.
It is the second set of leaked emails published by he Mail On Sunday Last week they revealed Sir Kim had described Mr Trump's administration as "inept" and "dysfunctional", a revelation that eventually led to the ambassador's resignation.
The paper said Darroch had written to the British government in May 2018 that Trump had chose to unilaterally withdraw from Iran's nuclear deal with major powers for "personality reasons", because it had been agreed by his predecessor Barack Obama.
In the cable, Darroch indicated there were splits among Trump's advisers and said the White House lacked a "day-after" strategy.
The former London mayor has been heavily criticised by MPs in his own party and the opposition for failing to defend Darroch after Trump attacked the envoy for leaked remarks describing the USA administration as inept.
Trump responded by calling Darroch "very stupid" and a "pompous fool" in a Twitter fusillade, and the White House cut off contact with the British envoy.
A British investigation into the leaking of confidential diplomatic memos is raising press freedom issues with a police warning, that United Kingdom media might face a criminal inquiry if leaked documents are published.
Darroch's defenders said his critical memos showed he was doing his job by providing candid assessments, as diplomats are expected to do, but he said the controversy had made it impossible to fulfill his duties.
The newspaper reported that, according to Darroch, Pompeo also hinted that he had tried but failed to "sell" a revised text to Trump.
According to the Sunday Times, which cited anonymous official sources, a suspect had been identified and the case was related to a computer hack.
The British police has also advised "all owners, editors and publishers of social and mainstream media" not to publish leaked government documents, whether they already have them or are offered to publish new ones.
The leaks sparked a furious argument Saturday between lawmakers and Britain's Metropolitan Police, who warned newspapers and broadcasters not to publish anymore of the cables or risk prosecution under the country's little-used Official Secrets Act.
Contentiously, police issued a warning to journalists that publishing the documents "could also constitute a criminal offence".
Mr Johnson said he had spoken to Sir Kim on Thursday to tell his disappointment over his resignation and the ambassador instructed him he had not watched the TV debate.
Meanwhile, leader of the opposition, Jeremy Corbyn said the leaks were: "Clearly a breach of confidence (and) information that should have been maintained as private".