Theon Monday could disrupt tourism in the U.K., even as British authorities step up security at airports and popular attractions including the Tower of London, Buckingham Palace and Parliament.
Prime Minister Theresa May, who on Tuesday warned that another terror attack "may be imminent," ordered as many as 5,000 troops to be deployed at "key sites" as she raised the country's threat level to its highest level of "critical." Members of the armed forces are replacing armed police officers who had been guarding these areas.
Tourism is an important industry in the U.K., accounting for more than 7 percent of the country's gross domestic product and employing nearly 2 million. Business boomed in 2016 as the number of visitors surged 7.2 percent, with Scotland, Wales, Northern Ireland all reporting a record number of visitors. According to the Tourism Alliance, the U.K. is the eighth-most visited country in the world by foreign visitors.
Americans account for the greatest number of tourists to the U.K., with spending of some $4 billion per year.
"All the U.K.'s visitor attractions have reviewed their own well-rehearsed, well-thought through security plans and procedures in the light of the change of the security level from 'severe' to 'critical'," wrote Bernard Donoghue, director of the Association of Leading Visitor Attractions, a U.K.-based tourism group, in an email. "Each works closely with their local police force's counter-terrorism officers, as we work with the National Counter-Terrorism Security Office of the U.K. Government. All of them work to ensure that these globally popular attractions are accessible, welcoming and safe for their visitors and staff."
Buckingham Palace, which has been home to British monarchs since 1837, along with London's historic Parliament, have been closed to visitors. The palace's traditional "changing of the guard" ceremony, a tourist draw for generations, has also been temporarily suspended. It wasn't clear how long the restrictions would continue.
Officials at Heathrow Airport have warned travelers of a "higher visibility of police patrolling and additional checks at the airport," though it expects overall operations to be normal. Passengers on two U.K. flights were recently evacuated after bomb scares were reported.
U.K. airports are no stranger to the terrorism threats. In 2006, a plot to blow up as many as 10 flights leaving London's Heathrow airport was thwarted by law enforcement. A year later, a Jeep loaded with propane was set on fire after being driven into Glasgow Airport, and incident that left five people injured.
Visitors to English Heritage, which manages 66 castles, 53 Roman sites, and Stonehenge among other attractions, are facing bag check and other additional security checks, according to a spokesperson. The sites under English Heritage's management remain open, and all events are going ahead as scheduled.
Historic Royal Places, which manages the Tower of London, has also tightened security.
"The security and safety of visitors to our places is our highest priority," a spokesperson for Historic Royal Places said in an email, declining to be more specific. "Following the decision to change the U.K. threat level to 'critical,' we have reviewed and increased security measures across our sites. These measures will continue to be subject to ongoing review."
Past terrorist attacks in France and Germany depressed business for some airline and hotel chains. Analysts caution that it's too early to say how the Manchester attack will affect tourism over the longer term. Not surprisingly, U.K. tourism officials are urging overseas visitors not to panic.
"We know that these tragic incidents can occur anywhere in the world, but in the U.K. we have a long history of dealing with security threats and we benefit from unparalleled intelligence expertise," Donaghue said. "As we have heard from the people of Manchester, the best response to those who would seek to frighten and intimidate us is to live our lives fully."
In the short term, the attack on Manchester Arena, which killed 22 people, is having repercussions. Soccer club Chelsea FC, winners of this year's Premier League season, announced Wednesday that it is canceling a planned victory parade in London both out of security concerns and out of respect for the victims of the attack. Another top-flight team, Arsenal, also said it won't hold a celebration if it wins the FA Cup final against Chelsea on Saturday. Both teams said they were mindful of the strain their events would cause the government at a trying time.