LONDON (AP) – Authorities downgraded Britain’s terror threat level Monday, offering hope to travelers mired in chaos at airports since security forces foiled an alleged plot to bomb trans-Atlantic jetliners. But more flights from London were canceled on the fifth day of the crisis.

Investigators focused on any links between the suspects in custody and associates in Pakistan, with suspicions raised that an Islamic charity funneled money raised for earthquake relief to help finance the alleged plot.

The threat level was lowered from critical to severe to reflect an intelligence assessment that a terrorist attack remained highly likely but was no longer imminent.

The critical level was declared last week when police rounded up two dozen people suspected of involvement in the terror plot. Police questioned all but one of the suspects Sunday, but authorities remained silent on what, if anything, they learned.

“I want to stress … that the change in the threat level does not mean that the threat has gone away,” Home Secretary John Reid said.

“There is still a very serious threat of an attack. The threat level is at severe, indicating the high likelihood of an attempted terrorist attack at some stage, and I urge the public to remain vigilant,” he added.

Those sentiments were echoed across the Atlantic by Homeland Security chief Michael Chertoff, who said Sunday there was a risk that other groups might try to cause bloodshed on the false assumption that law enforcement and intelligence services might be distracted.

He also called for taking a renewed look at U.S. laws that could give authorities the flexibility to detain suspects for longer periods of time. Britain recently passed controversial legislation giving the government up to 28 days to hold terror suspects without charge, and the jetliner plot is the first major test of how those new powers will be used.

With the reduction in the threat level, Britain’s Department of Transport said passengers would be allowed to carry a single, briefcase-sized bag aboard aircraft, and that books, laptop computers and iPods would be permitted again. However, Heathrow and other major airports said they would not adopt the relaxed regulations until Tuesday.

Officials at Heathrow said airlines canceled about 120 flights, 20 percent of its daily total. That was down from about 30 percent over the weekend, but dozens of travelers had to stand outside in the rain as guards limited the number of people entering terminals. Inside, thousands waited in lines that snaked through the buildings.

Ivana Djak, 16, a student from Columbia, Md., said she slept on her luggage Sunday night, using rolled up T-shirts for a pillow. “It was freezing,” she said.

Henry Burkett, 19, a student from Seattle, said he stood in line for three hours Saturday to check his luggage before his flight was canceled 20 minutes before its departure time.

“They don’t know where my luggage is at. Maybe in Seattle,” he said.

Meanwhile, a British Airways plane en route to New York returned to London after a cell phone on board began to ring and no one admitted owning it. The flight resumed after security checks, and arrived about seven hours late in New York.

Paul Marston, a British Airways spokesman, said the fact that the no one could explain how the phone got on the flight made the situation particularly suspicious. Cell phones _ along with all other electronic devices _ had been banned from cabins on flights out of Britain since Thursday.

Meanwhile, a court hearing to determine if police would be granted more time to question one of the 24 suspects arrested last week was expected to conclude later Monday. The 22 other suspects still in custody can be held until Wednesday. One suspect was released.

Police arrested the suspects in London and other English cities Thursday, saying officers had thwarted a plot to blow up as many as 10 passenger planes flying between Britain and the U.S.

London’s anti-terrorist police were searching a woodland area in High Wycombe, about 35 miles west of London, a police official said, speaking on condition of anonymity. The search would continue for at least 24 hours, though officers declined to say in anything significant had been discovered.

House of Lords member Nasir Ahmed said a member of the Muslim community told him that some of the people detained in the alleged plot went to Pakistan to assist with relief efforts after an earthquake killed nearly 80,000 people last year.

“It may be that out of 22, there may be a number of them who have met someone from extremist groups in Pakistan or Kashmir,” Ahmed said. “Some may have met them without knowing that they were meeting (extremists) because they were helping out in the aftermath of the earthquake.”

The New York Times reported that money raised for victims of the earthquake was channeled to the plotters through the Pakistani-based charity Jamaat al-Dawat _ a charge the charity denied.

The charity is not registered in Britain, but laws do not prevent British citizens from donating to or collecting for it.

An additional 17 people were detained in Pakistan, including Rashid Rauf, a British national named by Pakistani intelligence as one of the key suspects. Rauf was picked up along the Pakistan-Afghanistan border and is believed to have connections to a senior al-Qaida leader in Afghanistan.

In Kabul, Afghanistan’s Foreign Ministry on Sunday denied any Afghan connection to the plot, saying the country _ home to thousands of NATO and American troops _ was no longer a safe place for al-Qaida to operate.