Boris Johnson was reportedly denied access to some sensitive secret intelligence by Downing Street after he was appointed as foreign secretary.
The Conservative leadership frontrunner was said to have been denied full access to classified information when he entered the cabinet in 2016 amid fears he might reveal top-level secrets by accident.
Sources with “direct knowledge of events” told the BBC that Mr Johnson was cut out at Theresa May’s request, attributing the decision, in part, to “control freakery” at No 10.
The decision is said to have caused concern among intelligence officials due to the foreign secretary’s role in authorising sensitive operations.
Traditionally, the prime minister has overall control over the intelligence services but the foreign secretary oversees MI6 and GCHQ on a day-to-day basis.
Mr Johnson was said to have been aware of the decision at the time and “very unhappy” about it.
However a source in his camp said there was no row about being denied access and that he saw everything he should have seen as foreign secretary.
A Downing Street spokesman said: “We do not comment on intelligence matters.”
Nerves were sparked when Mr Johnson was accused of revealing classified information by mistake, according to The Sun.
A source said: “The PM didn’t think Boris could be trusted because he had a loose tongue. He made the agencies anxious. He wasn’t told everything because of that.
“Pre-meetings would be arranged without his knowledge before he’d come over to No 10.
“They probably both share the blame for the situation, and it was a clash of their worst traits – Boris is a big mouth and Theresa can be a paranoid control freak.”
The row comes as the Conservative leadership race enters its final stages, with Mr Johnson widely tipped to emerge as the victor at the end of July.
He will appear at four leadership hustings around the country over the next 48 hours, alongside his rival Jeremy Hunt.