The deputy prime minister made the warning amid fears that terrorists are working on a bomb that could sidestep current measures.
He said: “This is the world we now live in, this will not be the last time there are adjustments made because we are having to constantly evolve our own defences in response to ways that people want to attack us.
“I don’t think we should expect this to be a one-off temporary thing we have to make sure the checks are there to meet the nature of the new kind of threats.”
Changes to security measures were announced after Washington homeland security secretary Jeh Johnson ordered beefed-up security at foreign airports which have direct flights to the US, reportedly as a result of intelligence that groups in Yemen and Syria had joined forces to plot an attack.
Prime Minister David Cameron told the BBC: “We take these decisions looking at the evidence in front of us and working with our partners.
“This is something we’ve discussed with the Americans and what we have done is put in place some extra precautions and extra checks.
“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 that we always put safety first, and we do.”
The Government highlighted the importance of vigilance but said the extra measures — which have not been disclosed – are not expected to cause “significant disruption” to passengers and the official UK threat status remains unchanged at “substantial”, the third grade in the five-level rating.
Mr Clegg said: “I don’t want people to think that this is some sort of blip for a week. This is part of an evolving and constant review about whether the checks in our airports — and indeed other places of entry and exits from countries — keep up with what we know from intelligence and other sources about ... the threats we face.”
The increased security measures — reported to include closer scrutiny of personal electronics and footwear — come amid fears that individuals with Western passports who have travelled to Syria and Iraq to fight with Islamist extremists could be used to smuggle devices on to planes.
Intelligence is reported to suggest bomb-makers from Yemen-based al-Qaeda in the Arabian peninsula (AQAP) have travelled to Syria to meet al-Qaeda-affiliated Jabhat al-Nusra to work on ways to get an explosive device past existing security.
Al-Qaeda operatives in Yemen were behind an underwear bomb that failed to detonate aboard a jet over Detroit on Christmas Day 2009 and a more sophisticated version which was intercepted in a CIA sting operation three years later.
Saudi-born bomb-maker Ibrahim Hassan al-Asiri, believed to be a member of AQAP, was also said to be behind a powerful bomb hidden in printer ink cartridges which was intercepted at a UK airport en route to the US in 2010, where it was timed to detonate over the east coast.
Downing Street said there was an “evolving threat” and people should continue to fly but allow “appropriate time” to go through security.
The tightening of security came as a message was posted on a Twitter page purporting to be that of Nasser Muthana, from Cardiff, a British jihadi in Iraq, who appeared in an Isis propaganda video released last week. He tweeted, alongside a picture of containers: “So the UK is afraid I come back with the skills I’ve gained.”