Londoners asked to remain vigilant after Met police receive coded warning from dissident republicans Scotland Yard are investigating a “coded” bomb threat made against central London, on the eve of the Queen’s visit to Ireland. Police said on Monday that the warning did not give any details about the time or place of any device. The Guardian understands the warning was telephoned in to police late on Sunday afternoon by a caller claiming to represent the dissident republican cause. The caller used a codeword, although it was not recognised as being associated with any group. Officers are already on high alert over the “severe” terrorist threat from al-Qaida-inspired violence, with the threat from Irish terrorism judged by MI5 to be one level lower at “substantial”. News of the warning was passed to officers going out on patrol and made public by police at lunchtime on Monday. The Metropolitan police said: “A bomb threat warning has been received relating to central London today. The threat is not specific in relation to location or time. “The Metropolitan police service, City of London police and British Transport police are working closely together and all officers have been advised to be a highly vigilant to ensure the safety of London. Policing operations and contingency planning remain under constant review and a wide range of overt and covert tactics will continue to be used in London. “At this time Londoners should continue to go about their business as usual but we encourage the public to remain vigilant and report any information about unusual activity or behaviour which may be terrorist-related to the confidential anti-terrorist hotline on 0800 789 321.” There was a large-scale security alert near Buckingham Palace on Monday morning. Roads around the Admiralty Arch area of the Mall were reopened before noon after a security scare in the early hours. A painstaking search was launched and roads were closed around the ceremonial gateway that leads from the corner of Trafalgar Square after an officer spotted “something suspicious” at 4.20am. There was also understood to have been a controlled explosion of a suitcase in nearby Northumberland Avenue as officers swooped on suspicious packages. The threat level from Irish-related terrorism has not been raised after the codeword warning to police. Coded warnings were often used by Irish terrorists in their campaign of violence against the British mainland. A hallmark of al-Qaida-inspired violence is the lack of any warning. UK security and terrorism Northern Ireland London The Queen Metropolitan police Police Vikram Dodd guardian.co.uk