Hours before Queen Elizabeth's historic visit to Ireland dissident Irish Republicans have made a bomb threat in central London.
The Associated Press has reported that the London Metropolitan Police received a bomb warning on Sunday evening. The warning did not include a specific location or time.
A Scotland Yard spokesman said: 'A bomb threat warning has been received relating to central London today. The threat is not specific in relation to location or time.'
Police officers conducted sweeps across the city, closing down traffic in parts of the city, including those around the official residence of the Queen. Roads around the Admiralty Arch, the Mall leading to Buckingham Palace and the area around Trafalgar Square were all closed off while searches were in progress.
A police statement read "Londoners should continue to go about their business as usual but we encourage the public to remain vigilant."
Although this is the first serious threat to Britain's mainland from dissident Republicans in several years it was predicted as violence has been escalating in Northern Ireland.
Police added that the official threat level has not increased and remains at a substantial level. They believe an attack is strong possibility.
The last successful attack on Britain by the dissident Republicans was in August 2001. A car bomb exploded near a shopping center in west London, wounding 11 people. In 1993 a bomb in London's financial district killed one person and wounded 44.
In Ireland troops with ground-to-air missiles are being deployed in preparation for the Queen's visit on Tuesday.
Her historic visit was encouraged by the largely successful peace process in Northern Ireland. She will be the first British monarch to set foot in the Republic of Ireland.
Security for the Queen's visit will be greater than the measures used for the 1979 visit of Pope John Paul II and for the 1990s visit of US President Bill Clinton.