Britain and other countries fighting terrorists also should establish a multi-level, antiterror system of cooperation and information exchange on bilateral, regional and global levels, Li said.

"We do now need more information flowing internationally about who are potential terrorists and who are potential suspects," Brown told Sky News television on July 8, the day after the anniversary of the 2005 suicide bombings in London.

Different countries have different opinions on why and how terrorism grows, and it is very tricky for the world to reach a common understanding on determining which forces are terrorist ones and which are not, Li added. Countries need to settle this issue immediately with the United Nations leading the effort before they can succeed in building global antiterror networks, he said.

"The double standard on terrorism is one of the big obstacles to knitting such systems," he said.

The antiterror battle can last for generations, and it will be impossible for a single country--even one as powerful as the United States--to win it alone, Li said.

Alan West, the former British navy chief who was appointed by Brown as his security adviser, said that Britain's battle against the terror threat could last for 15 years, The Sunday Telegraph newspaper reported.

He Weibao, a scholar with the Institute of American Studies at the Chinese Academy of Social Sciences, agrees that weaknesses in countries' security policies and systems have allowed terrorists to penetrate them.

Islamic extremists have been taking their time to study the security systems of both Britain and the United States in order to try to penetrate them and carry out attacks, He said.

He also believes that Britain's antiterrorism strategy, which is similar to the American one in focusing on Islamic extremists, has incited hatred among the extremists and provoked the recent attacks in Britain. Most British citizens cannot understand why these extremists hate the country so much, he added. After the latest attacks, the Muslim Council of Britain issued a statement telling Muslims it was their Islamic duty to cooperate with police to ensure the country's safety.

Some analysts in Britain echoed the sentiments of the Chinese experts.

People need to be constantly vigilant against what is a long-term and sustained threat, said a report on the British Sunday newspaper The Observer, "We have to fight it in a number of different ways: militarily, by security, by police, by intelligence."

British police defused two car bombs in London on June 29. The two cars, packed with petrol, gas canisters and nails were found a short distance away from each another in a centrally located shopping area.

The next day, a blazing jeep crashed into the main terminal at Glasgow Airport in Scotland. Police later announced that the two incidents were related terrorist acts by people associated with Al Qaeda, aimed at creating a large number of casualties. Britain then raised its national security alert level to "critical."

No one was killed in either incident.

The attempted terrorist attacks came at a time when an influx of people were attending different events in the London area, including the city's annual gay pride parade, a concert commemorating the 10th anniversary of the death of Princess Diana and the Wimbledon tennis championships. The bomb scares reminded Londoners of the suicide bombings on the city's public transport system on July 7, 2005, when 52 were killed and more than 700 injured. They also recalled the plot by Islamic extremists to detonate bombs on tube trains and a bus in London on July 21 of that year.