Airport security around the world will have to be overhauled if it is confirmed the Russian airliner crash in the Sinai was caused by an Islamic State bomb, Foreign Secretary Philip Hammond has warned.
Egyptian investigators have reportedly said they are 90% sure a noise picked up by the cockpit voice recorder in the final seconds of the flight was the sound of the explosion caused by a bomb.
The investigation committee has yet to formally declare its findings, but Mr Hammond reaffirmed that the view of the British authorities is that it was "more likely than not" that the crash was the result of a terrorist bomb planted on the aircraft before it took off from Sharm el-Sheikh eight days ago.
And he said there would have to be a major re-think of airport security in countries where IS - also referred to as Isil of Isis - is active if it turned out that they were behind the attack.
"If this turns out to be a device planted by an Isil operative or by somebody inspired by Isil then clearly we will have to look again at the level of security we expect to see in airports in areas where Isil is active," he told BBC1's The Andrew Marr Show.
"What we have got to do is ensure that airport security everywhere is at the level of the best and that airport security reflects the local conditions and where there is a higher local threat level that will mean higher levels of security are required.
"That may mean additional costs, it may mean additional delays at airports as people check in."
Mr Hammond said British tourists waiting to get out of Sharm el-Sheikh following the Government's decision to end flights to the UK could experience a delay of "two or three days".
The Foreign Secretary also suggested the incident could open up the possibility of renewed co-operation between the West and Russia on Syria where Islamic State is concentrated.
"On this particular issue - Syria and Isil - we see eye-to-eye with the Russians on lots of things," he said.
"Our vision for a future Syria is broadly similar. The need to destroy Isil - the Russians completely agree with us. They have got a very large Muslim population in the Russian Federation, they are very alert to the risks of radicalisation."
He acknowledged, however, that major differences remained on the future of Syrian President Basher al Assad, who the West insist must go as part of any settlement to the country's bloody civil war.
"What would be perfect would be if Mr Assad was to wake up one morning and decide that he didn't want to do this job any more," he said.
"The one person who has the power to persuade him that is in his country's best interest is President Putin. I hope that at some point in this process he will decide to do that."
Meanwhile thousands of Britons remain stranded in Sharm el-Sheikh as strict security measures at the resort's airport have delayed flights to bring them home from their holidays.
Tourists returning to the UK described chaotic scenes, with people trampled and hurt as they rushed for planes while swamped security staff carried out only cursory checks.
Crash investigators have revealed the unidentified noise was picked up by the doomed aircraft's on-board recorders in the final second before it broke up suddenly in mid-flight over Egypt's Sinai Peninsula eight days ago.
Lead investigator Ayman el-Muqadem said they were looking at "all possible scenarios" as to the cause but confirmed the Airbus 321 was still gaining altitude as it disintegrated 23 minutes after take-off, killing all 224 people on board the Metrojet flight.
He said: "It could be lithium batteries with one of the passengers, it could be an explosion in the fuel compartment - all the scenarios are on the table, I cannot exclude anything."
In an apparent dig at countries like the UK and the US, which Egyptian authorities say have refused to share intelligence, Mr el-Muqadem asked for any information to be shared openly.
He said: "The (investigatory) committee noted media reports and analysis - some of which claimed to be based on official intelligence - which favours a certain scenario for the cause of the accident. The committee was not provided with any information or evidence in this regard.
"The committee urges the sources of such reports to provide it with all information that could help us to undertake our mission."