A Whitehall source said: “Malik Akram was known to MI5 and was the subject of a short lead investigation in 2020.

“The investigation was opened in the second part of 2020 and was closed shortly afterwards with an assessment that there was no indication he presented a terrorist threat at that time.”

At any one time, MI5 has about 3,000 jihadist suspects under active investigation, known as subjects of interest (SOI). There are between 30,000 and 40,000 individuals who have come across MI5’s radar, but are no longer being investigated. 

Akram was in the latter category at the time he chose to fly to the US.

“He was a closed SOI and so there were no grounds for further examination and no basis to prevent him travelling,” a source said. 

Intelligence agencies said it would be disproportionate to prevent tens of thousands of people from travelling abroad, effectively depriving them of their liberty, on the basis of individuals having been brought to their attention at some stage.

Akram did not ‘pass threshold’ for full investigation

It is understood that after more than a month of active investigation, intelligence officers decided Akram did not “pass the threshold” for a full-blown, further investigation. 

MI5 stresses it has limited resources and is unable to put every suspect, out of thousands, under manpower-intensive, full-blown surveillance.

The Whitehall source said MI5 would now look at Akram’s case to see if anything should have been done differently. 

There remain questions over how Akram was able to enter the US on a tourist visa. His criminal history dates back to 1996 when he was jailed for violent disorder following a baseball attack on a member of his extended family. 

Gulbar Akram, his brother, questioned why authorities had let him in given he was known to UK police, and had a long criminal history and mental health problems.

A US official told The Telegraph there was no information on the country’s intelligence databases to suggest Akram should be denied entry.