Arrests in Britain underline security jitters before Olympics

Authorities say none of the alleged plots are linked to London's pending Olympic Games, which begin on July 27. However, many experts believe police and intelligence officials are becoming increasingly cautious as the event approaches.

"The government is simply not prepared to take any risks ahead of the Olympics," said Tobias Feakin, a security expert at the Royal United Services Institute think tank. Under usual circumstances, authorities often monitor plots for weeks or months to gather evidence - rather than swoop in immediately to arrest the suspects.

Outside of Northern Ireland, the number of people arrested on suspicion of terrorism offenses has fallen sharply in the past 12 months. In 2011 there were 167 arrests in England, Scotland and Wales related to terrorism offenses - the lowest figure since 2001. It compares with an average between 2002 and 2010 of 217 arrests per year. A total of 47 people were charged with a terrorism offense in 2011 - about 27 percent of those arrested, and in line with the rates for other crimes. In Northern Ireland, which collects its arrest figures separately, a total of 159 people were detained on suspicion of terrorism between April 2011 and March 2012 - 39 were eventually charged in that period, or 24 percent.

Britain currently ranks the threat from international terrorism as substantial - the middle point on a five-point scale, which means intelligence agencies believe an attack is a strong possibility, but not imminent. The level was last raised to critical - the highest level - in June 2007. David Anderson, terrorism laws ombudsman for Britain's government, says the threat has "reduced significantly in recent years." However, he also warns that "recent improvements in the security situation on both sides of the Irish Sea are not irreversible."

Suspects can be detained over a wide range of terrorism offenses - from suspicion of preparing to carry out, to initiate or direct a terrorist attack; preparing weapons or other planning for terrorism; possessing documents about terrorism, like bomb-making guides; raising funds; attending or organizing terrorist training camps; distributing terrorist books, videos or websites, or an offense of encouraging others to carry out terrorism. Membership of any of 62 groups banned in Britain as terrorist organizations is also an offense.

Since taking office in 2011, Britain's coalition government has rolled back some of the country's most draconian anti-terrorism laws. Police now have up to 14 days to hold terrorism suspects - down from 28 days - before they must be charged with a crime or released.

In contrast, U.S. authorities have only seven days and French police only six to bring charges. Ex-British Prime Minister Tony Blair lost a 2005 Parliamentary vote seeking to set the limit at 90 days.

A system of house arrest for some suspects who cannot be charged with any offense - typically because to do so could jeopardize an intelligence source - has been scaled back. Authorities can order a person to stay at a specific address overnight, and restrict their contact with certain people, but the program is now limited to two years - previously it had been indefinite.

Police no longer have powers to conduct random public searches on anti-terrorism grounds, while more stringent laws govern the retention of DNA or fingerprints.

When people are arrested on suspicion of terrorism - just like with any other crime in Britain - police publicly announce the age and genders of those arrested, details of addresses where they were detained and other locations being searched. Police also announce the alleged offenses carried out, but typically this is restricted to the brief legal definition and does not include detail of the specific case. If suspects are charged, prosecutors then outline more details at an initial court hearing before a judge. However, much of this can't be immediately disclosed under laws which seek to ensure the suspects receive a fair trial and that potential jurors at any future hearing haven't already been swayed by detailed accounts in the media.