Daniel Abed Khalife used heavy duty straps to cling to the underside of the food delivery vehicle when it left HMP Wandsworth on Wednesday morning.
When it was stopped by police with sniffer dogs over an hour later, all officers discovered were the abandoned straps.
Scotland Yard said there have been no confirmed sightings since of Khalife, a former British Army soldier, and have warned that his special skills and military training may make him extremely difficult to locate.
A huge manhunt was continuing on Thursday night with the fallout surrounding his prison break-out ongoing.
No trace of escapee
Commander Dominic Murphy of the Met’s counter terror unit said it was clear that the escape had been carefully planned and he did not rule out that Khalife may have had help.
He said: “This was a really busy area of London and we’ve had no confirmed sightings in any of that information, which is a little unusual, and perhaps testament to Daniel Khalife’s ingenuity in his escape and some of his movements after his escape.
“It’s important that we remember that we have some of the best military in the world here in the UK and he was trained.
“He was a trained soldier – so ultimately he has skills that perhaps some sections of the public don’t have.”
Meanwhile Alex Chalk, the Justice Secretary, ordered an urgent investigation into the escape and asked officials to explain why Khalife, who is suspected of terror offences and spying for Iran, was being held in a Category B prison.
Following the apparent blunder, the security level of all 271 terrorism prisoners as well as all the inmates in HMP Wandsworth is to be reviewed.
More than 150 counter terror specialists have been drafted in to help with the search for Khalife amid fears that he may have already fled the country.
Extra checks at the Port of Dover on Thursday led to the M20 motorway being temporarily closed.
The mystery of his continued disappearance has led to speculation Khalife may have been receiving support.
“He is unlikely to have had a change of clothes or mobile phone but has vanished into thin air. He must have had outside help,” said one prison chief.
The escape has raised major questions over systemic failings at Wandsworth prison.
Jail suffered a virtually identical escape
The Telegraph can reveal that the jail suffered a virtually identical escape by a prisoner four years ago when an inmate clung onto the underside of a prison van attempting to abscond from the jail.
Senior prison chiefs believe “human error and sloppiness” were exploited by Khalife, who is thought to have spent weeks planning his escape after securing a “plum job” in the prison kitchens.
Any inquiry is expected to examine the role of operational support grade (OSG) staff who are required to search vehicles – underneath, using mirrors, on top and inside – before allowing it to leave the prison.
Despite the security posts being fully staffed on Wednesday morning, the officers’ spot checks failed to detect Khalife.
Sources claimed that OSG staff are so stretched that some are being deployed without even having the basic three week security training course.
HM inspectorate of prisons and local watchdogs have consistently warned over the past two years that Wandsworth prison’s performance was “of serious concern” with staff absences of more than 30 per cent and most officers having less than two years’ experience, leaving them desperately short of “prison craft”.
Conditions were so bad that, earlier this week, it emerged that a German court had refused to extradite an Albanian suspected money launderer to the jail because of its poor conditions.
An upgrade of its CCTV cameras should have been completed two years ago, but has been delayed until 2025.
Speaking in the House of Commons, Mr Chalk vowed that Khalife “will be found and will be made to face justice”.