LONDON (AP) - Around the world, watch lists are a key tool against terrorism - but highly imperfect.

Experts say simple issues like fickle spelling and incomplete data, as well as deliberate deception and uncooperative countries, all make it possible for a determined terrorist like bomb suspect Umar Farouk Abdulmutallab to slip across borders.

British officials are proud of their list, which contains more than one million names, including that of Abdulmutallab. That didn’t stop the young Nigerian boarding a flight from Amsterdam to the United States with explosives in his underwear, a stark reminder of the perils of flawed information-sharing and the limits of watch lists.

``Lists are valuable in making sure governments around the world are able to track individuals,’’ said John Harrison, an aviation security specialist at Singapore’s S. Rajaratnam School of International Studies. ``But you don’t want to put too much emphasis on these lists. It’s an overstatement to say: ‘OK, now we are safe.’’’

Analysts say human intelligence, information-sharing and data analysis are also vital to stopping terrorists, and Britain has announced an urgent review of its watch list system in the wake of the Christmas Day attack over Detroit.

The British list holds the names of everyone from suspected terrorists and radical clerics to wanted criminals and rejected visa applicants, like Abdulmutallab, who was added after being denied a student visa in May 2009 for listing the name of a bogus college on the application.

The list is the centerpiece of a program called E-borders, which will eventually check all passengers traveling to or through Britain against the master list. Information comes from police, intelligence services and other sources and is held by the UK Border Agency.
Home Secretary Alan Johnson said this week that the list had led to almost 5,000 arrests since 2005, mostly for crimes such as murder, rape and assault rather than terrorism, and prevented 65,000 people entering Britain in 2009.

``In some countries, there are separate watch lists for security, for policing and crime, for people who have lost their passports and for immigration issues, but an integrated watch list serves us well,’’ Johnson told lawmakers in the House of Commons.

Magnus Ranstorp, a terrorism expert at the Swedish National Defense College, said the British system was an effective deterrent.

In the UK, he said, every passenger coming into the country is scrutinized. ``Even if you are in transit, and never meet a border guard, it’s a hostile environment if you’re flying through the UK,’’ he said. The list has its limits, though. Names on it are not automatically shared with other countries, although those on a smaller terrorism-related watch list are.