LONDON — Thousands of extra police are patrolling London's streets ahead of this week's Group of 20 summit amid fears that terrorists could capitalize on the presence of tens of thousands of unruly protesters to launch an attack.
The convergence of the two threats comes as Britain already is at a "severe" level of alert, meaning security officials believe an attack is highly likely. Bankers are being warned to dress casually _ to deflect populist anger aimed their way _ and luxury hotels are securing their perimeters for fear they could be targeted.
Concern is particularly high because the last major summit in Britain _ the Group of Eight meeting in July 2005 _ was marked by deadly suicide attacks on London's transit network that killed 52 people.
"We will be challenged. We will be stretched," said Simon O'Brien, a senior police commander responsible for the 7.2 million pound ($10 million) operation to secure the city during the meeting.
Tens of thousands of demonstrators plan four days of protests at sites across London, threatening to overwhelm police and potentially leave the British capital more vulnerable. Britain's home secretary, Jacqui Smith, said that while no specific plot against the G-20 summit had been identified, terrorists could strike "without warning at any time."
Michael Clarke, the head of London's Royal United Services Institute think-tank, said small terrorist groups may use the cover of planned protests by environmentalists, anti-war protesters and labor unions to mount an attack.
"The protests will cause uncertainty and chaos, and if they turn violent could complicate the lives of those police and security service staff who are looking for terrorists," said Clarke, who sits on British government's National Security Forum, an advisory panel of security experts.
Police arrested five people in the southern England town of Plymouth 240 miles (385 kilometers) from London on Monday under terrorism laws and recovered a haul of replica weapons, fireworks and activist propoganda. Law enforcement officials said officers are investigating whether the group planned to target the summit.
Around 5,000 police _ some armed with Taser stun guns _ will guard London, and an extra 35,000 will be on standby for the summit on Thursday. Some will be stationed at the summit venue in London's docks district, with others protecting swank hotels and the sleek glass towers of the city's financial district.
Following November's seaborne attack on Mumbai, India's financial center, extra patrol boats will guard the steel gray waters of the River Thames, and police frogmen will scour the river's length for floating bombs.
Police will tap London's network of 10,000 CCTV cameras to monitor protests, while an army special forces unit will be on alert to respond.
Protesters have threatened to train their anger on the city's financial center, urging demonstrators to "Bash A Banker" and "Storm The Banks" in leaflets promoting their rallies.
Banks and hotels have prepared for attempted raids or sieges on their buildings, said Pepe Egger, a senior security analyst at London's Exclusive Analysis Ltd.
He said that unlike previous summits _ including demonstrations outside a G-8 summit in Genoa, Italy in 2001 _ most protests in London will be away from the actual meeting venue at the city's ExCel center.
"The interesting thing is that the protesters are unlikely to target the G-20 delegates, their anger is not directed at the G-20 itself. They will target the banks and the financial district," Egger said.
Anger at bankers is high in both Britain and the United States, where some of the public funding to rescue stricken banks has been used to pay staff bonuses. The home of Fred Goodwin, the ex-head of Britain's Royal Bank of Scotland, was attacked last week.
Banks have told staff to dress in causal clothes on Wednesday and Thursday, to forgo cigarette breaks outside bank headquarters, and to cancel all but their most critical meetings.
"I'm pretty worried," said Luke Keyser, a 28-year-old banker at the Royal Bank of Scotland. "We've already been told to dress down. If we want to, we can work from home."
Associated Press Writer Martin Benedyk contributed to this report.