Downing Street attempted to withhold sensitive intelligence from Boris Johnson when he became foreign secretary, the BBC has learned.
This caused concern in the intelligence services, since the foreign secretary authorises sensitive operations.Sources close to Mr Johnson said he had access to everything he needed to see.
The Conservative leadership frontrunner told activists he was "extremely dubious about the provenance of the story", claiming it was "not true".
Pressed about the issue at a Conservative leadership hustings in Darlington, Mr Johnson said he would not comment further on national security issues.
A Number 10 spokesperson said it did not comment on intelligence matters.
On 20 October 2016, Mr Johnson paid his first visit as foreign secretary to MI6's headquarters at Vauxhall Cross in London.
After he was shown around by Alex Younger, the chief of MI6, Mr Johnson addressed staff and held an informal question and answer session."I was delighted to welcome the foreign secretary to our Vauxhall Cross headquarters so he could see first-hand the kind of work that MI6 does," the chief, known as "C", said at the time.
Mr Johnson was effusive in his praise.
"Even from my relatively short period as foreign secretary I can testify to how vital the work they do is," he said.
It is understood that Theresa May and some in the intelligence community had worries about Boris Johnson's ability to keep information confidential.