The United States is requesting tighter security checks on fights to America in response to concerns extremists are developing undetectable bombs to put on planes.
The move is thought to be due to intelligence reports that Islamist groups in Yemen and Syria have joined forces.
Speaking to Premier's News Hour, Simon Barrett, a Christian and expert on matters of terrorism, says there are real concerns:
Passengers are being told to expect delays at airports although it's not clear what form the extra checks will take, but it's understood passengers are being asked to take all electrical and battery-operated items out of their bags to be scanned.
Prime Minister David Cameron said security had to be the priority: "The safety of the travelling public must come first, we mustn't take any risks with that.
"I hope this won't lead to unnecessary delays but it's very important we always put safety first and we do".
The Department for Transport has issued a statement: "We have taken the decision to step up some of our aviation security measures.
"For obvious reasons we will not be commenting in detail on those changes. The majority of passengers should not experience significant disruption. There will be no change to the threat level, which remains at substantial".
US Department of Homeland Security Secretary Jeh Johnson said the increased measures were in response to a real and credible threat: "We will work to ensure these necessary steps pose as few disruptions to travellers as possible.
"We are sharing recent and relevant information with our foreign allies and are consulting the aviation industry.
"These communications are an important part of our commitment to providing our security partners with situational awareness about the current environment and protecting the traveling public.
"Aviation security includes a number of measures, both seen and unseen, informed by an evolving environment."
Meanwhile, US authorities are warning of a specific terrorist threat to Uganda's only international airport.
Intelligence sources think there's a risk from an unknown group today. They're warning travellers not to use Entebbe International Airport.
In December 2009, Nigerian Umar Farouk Abdulmutallab detonated an undetectable bomb in his underpants on a flight between Amsterdam and Detroit.
It failed to detonate properly and only he was injured.
Then in October 2010, two undetectable bombs were found hidden inside printer cartridges on cargo flights at Dubai and East Midlands Airport.