BRITAIN will unite to pay tribute to fallen troops today as Remembrance Sunday services are held across the country.

The Queen will take part in a ceremony at Whitehall's Cenotaph in central London where she will lay a wreath in memory of members of the armed forces killed in major conflicts.

The event is the focal point of the country's Remembrance Sunday ceremonies and will see other senior royals and political leaders also leave floral tributes at the memorial.

Scotland Yard said it had an "appropriate and proportionate" policing plan in place for the event amid heightened fears of a terror attack.

It comes after four men were arrested in west London and High Wycombe in connection with an alleged Islamist terror plot on British soil on Thursday night.

Prime Minister David Cameron said this year's Remembrance Sunday was "particularly poignant" as 2014 marked the 100th anniversary of the start of the First World War, the 70th anniversary of the D-Day landings and the end of Britain's conflict in Afghanistan.

He said: "Today we stand united to remember the courageous men and women who have served our country, defended our freedoms and kept us safe.

"We remember all those who have fallen and those who have risked their lives to protect us.

"We owe each and every member of our armed forces and the families who support them a tremendous debt - one that can never be repaid - and I pay huge tribute to their bravery and resolve."

The ceramic poppy field at the Tower of London was an "incredibly moving, yet stark reminder" of how many people gave their lives in the First World War, Mr Cameron added.

It was announced yesterday that the wave section of the artwork - which will have 888,246 ceramic poppies installed by Armistice Day, one for each British and colonial death during the conflict - will remain on show until the end of the month.

The Queen will be joined by the Duke of Edinburgh at the Cenotaph in Whitehall , according to the official website of the British Monarchy.

The Prince of Wales and Duchess of Cornwall will also attend, along with the Earl and Countess of Wessex, the site said.

A two-minute silence at the heart of the service will be marked at the beginning and end by the King's Troop Royal Horse Artillery firing one round from one of their 13-pounder First World War guns from Horse Guards Parade.

Meanwhile, as dusk falls, images of falling poppies are to be projected on to Parliament's Elizabeth Tower - popularly known as Big Ben - as part of commemorations of the centenary of the conflict.

A service will also be held at the National Memorial Arboretum in Staffordshire, before wreaths are laid at the stone armed forces memorial.

Since last year's Remembrance Sunday, seven members of the British armed forces have died on operations.