Four Islamic terror suspects arrested in west London and the Home Counties Officers from terrorism command seized men after months of surveillance It comes ahead of events honouring the nation's war dead on Sunday Police warned that Parliament and London landmarks could be terror targets Officers will step up security as Queen leads events to mark WWI centenary One of the suspects, a 27-year-old, arrested by armed police in the street Remaining three men, aged 22, 19, and 25, were held at different addresses The home of Yousaf Syed, the 19-year-old suspect, had been raided before Scotland Yard says the arrests are linked to 'Islamist related terrorism' Raids in High Wycombe, Hounslow, Uxbridge and Southall, west London Officers are also searching eight properties linked to the arrested men By Chris Greenwood and James Slack for the Daily Mail and Martin Robinson for MailOnline Four Islamist terror suspects were being held by police last night amid fears of a Remembrance Sunday gun plot. Armed officers seized the men following months of surveillance and ahead of events honouring the nation's war dead tomorrow. Police had already stepped up security after a terrorist shot a soldier guarding a war memorial at Canada's parliament. And a ring of steel will be thrown around Whitehall tomorrow as the Queen leads events at the Cenotaph marking the centenary of the start of the First World War. Terror raids: Four men have been arrested in a series of terror raids, including one here in High Wycombe, Bucks, amid fears A police officer guards this property in Desborough Avenue, where a neighbour said officers were searching a shed. The timing of the raids raised fears of a Remembrance Day outrage Although police would not discuss whether the suspects had a specific target, the timing of the raids raised fears of a Remembrance Day outrage. Islamic State militants have called on "self-starter" followers to target high-profile commemorative events. The suspects, aged 19 to 27, were being questioned last night on suspicion of preparing terrorist acts. Police marksmen from its SO15 terrorism command arrested the youngest suspect on Thursday night at the home he shares with his mother in High Wycombe, Buckinghamshire. He is said to have recently returned from Pakistan. In an unusual move, the eldest suspect was stopped at gunpoint in his car in Southall, West London, but no shots were fired. The other two were arrested in Hounslow and Uxbridge and searches were taking place in Greenford and Hayes, also in West London. The suspects were all arrested on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism. It was reported the allegations are linked to a UK plot - not travelling to Syria to join ISIS. A ring of steel will be thrown around Whitehall tomorrow as the Queen leads events at the Cenotaph to mark the centenary of the start of the First World War The use of armed officers for the arrests suggests police chiefs fear the suspects may have acquired weapons. None were found, however. The Metropolitan Police said the operation involved its counter-terrorism command, MI5 agents and officers from other constabularies. The home of Yousaf Syed, the 19-year-old suspect, had been raided before - in April during an investigation into potential jihadists. Another man arrested in that operation complained his passport was seized by the Home Office to stop him travelling to the Middle East. Neighbours of Syed said he lives with his 41-year-old mother Somia, who works as ground crew for an airline. One said he had had "several run-ins" with the "angry" teenager. When he challenged the teenager's mother, she told him: "I'm sorry, it's my son. He's young and he's just discovered his faith. The neighbour said the teenager recently grew a full beard and began wearing traditional Muslim dress. Another resident said officers removed items from the garden shed as forensic officers combed the house and garden. Today two police officers wearing high visibility jackets were posted outside the brown wooden front door of the brick terraced house in Desborough Avenue, near the town centre. A cordon of police tape was placed around the brick driveway to the home, on which a police patrol car was also parked. All the curtains were closed at the terraced house where police forensic staff were combing the home and garden for clues while neighbours stood in the street and watched. Investigation: These officers were guarding the front door of this High Wycombe house while forensics worked inside The neighbour said that he saw a woman, the teenager, a man aged in his 20s along with two small children regularly coming and going from the address. He said that he had been out when the raid took place early this morning and that he arrived back at his home to find officers removing items from the family's shed. Two other addresses in the town were being searched, including a rented flat and a £300,000 house apparently occupied by Syed's aunt. High Wycombe's remembrance parade is due to take place at 10.30am tomorrow in the high street before proceeding to All Saints" Church. Raids: Scotland Yard said that they have arrested four young men in a series of raids linked to an alleged Islamist terror plot It attracts large crowds, in part due to the proximity of the town to RAF High Wycombe in nearby Naphill. A large contingent of personnel from the base, which is the home of the RAF's Headquarters Air Command, traditionally marches with veterans and other community groups. Germaine Lindsay, who killed 26 people when he detonated a bomb on the Piccadilly Line in the 7/7 attacks, has links to High Wycombe. There are growing concerns that British jihadists fighting in Syria and Iraq will return to this country and carry out acts of terrorism. But detectives do not believe there is any direct link between the latest arrests and fanatics in the Middle East. David Cameron ordered a security review last month after the Canadian attack. Heads of MI5 and Scotland Yard held talks over the terror threat to Parliament and other landmarks in central London. Just a few weeks ago police were warned to be on their guard over fears they could become targets. In London, frontline officers were warned of intelligence that suggested terrorists aspired to abduct and murder a policeman. In August the national terror-threat level was raised from substantial to severe, meaning a terrorist attack was "highly likely." A Metropolitan Police spokesman said the men were being held on suspicion of "being concerned in the commission, preparation or instigation of acts of terrorism." He said the arrests were part of an ongoing investigation by the Met's counter terrorism command, colleagues from other forces and MI5. He added: "They have all been taken to police stations in central London and remain in custody. Two of the entries to premises were assisted by firearms officers. No shots were fired. On Remembrance Sunday in 1987, 11 people were killed and 68 wounded when the IRA bombed the cenotaph in Enniskillen, Northern Ireland. This year's Armistice Day will be used to mark the centenary of the start of the First World War and the withdrawal of British troops from Afghanistan.