Sir Olly Robbins said it was deeply worrying that the story was given to The Guardian.
An inquiry into the leak of information relating to Lord Peter Mandelson’s security vetting is under way, the Government has said.
Information was given to The Guardian after the Cabinet Office briefed Number 10 on the matter.
Responding to an emergency debate on the appointment of Lord Mandelson as US ambassador, Chief Secretary to the Prime Minister Darren Jones told the Commons: “I am sure the House will be as concerned as I am that whilst officials felt unable to provide this information to ministers, this information was made available to The Guardian newspaper.
“As a consequence of that, I can confirm that a leak inquiry is now under way.”
Sir Olly Robbins, who was sacked by the Prime Minister over the failure to disclose Lord Mandelson’s failed security checks, said it was deeply worrying that the story was given to the newspaper.
“I’m not making accusations at anybody, it’s not my business to do so,” he told the Foreign Affairs Committee, adding: “I hope they’re being very rigorously investigated, and that prosecutions will result, because this is a grievous breach of national security.”
