Encouraged by the largely successful peace process in Northern Ireland, the queen on Tuesday will become the first British monarch to set foot in the Republic of Ireland, where troops and even ground-to-air missiles were being deployed amid tight security for her visit.
When a British sovereign last visited, a full century ago, all of Ireland was still part of the United Kingdom.
The monarch’s presence is resented by some in Ireland who bristle at the legacy of British rule, with some predicting violent street clashes and others fearing a terrorist attack.
London’s Metropolitan Police said the bomb warning, which was received late Sunday, did not include a specific location or time.
Officers were conducting sweeps across the city and closed down to traffic parts of the British capital, including roads near Buckingham Palace, the queen’s official residence.
“Londoners should continue to go about their business as usual but we encourage the public to remain vigilant,” police said in a statement.
A police official who spoke on customary condition of anonymity in line with policy confirmed that the warning related to a threat from a dissident Irish republican group.
The bomb warning was the first serious threat to Britain since 2001, the last time republican dissidents made a successful attack in England, exploding a car bomb near a shopping center in west London, wounding 11 people.
“The threat level to Great Britain from Northern Irish-related terrorism remains at substantial, which means that an attack is a strong possibility,” the Home Office said in a statement. “There is a continuing need for vigilance and the public should report any suspicious activity to the police.”
The national police force has canceled all leave and drafted in officers from rural areas, boosting the security detail to 8,500. They also have borrowed two mobile water cannons from Northern Ireland’s police.
The queen’s four-day trip to Dublin, Kildare, Tipperary and Cork comes as a Catholic-Protestant government in the neighboring British territory of Northern Ireland has just been re-elected, marking another peace milestone.
The Irish Republican Army violence of decades past — counting among its victims the queen’s cousin, Lord Louis Mountbatten, killed when the IRA blew up his yacht in 1979 — has given way to the group’s 2005 renunciation of violence. Only small splinter groups still plot bloodshed across the border.