The Duke of Cambridge meets veterans at the Korean War Memorial in London, 5 November 2013.
Wearing a poppy has become a symbol of remembrance, for all the fallen soldiers of WWI.
The Canadian doctor John McCrae wrote the poem In Flanders Fields in memory of his fallen comrades: “the poppies blow / Between the crosses, row on row..” It describes the first sign of life after death - small red plants that grew on the graves of soldiers in the battle fields of Northern France and Flanders during WWI.
The poem inspired American secretary Moina Michael to sell poppies to raise funds for ex-soldiers.
It soon became the US national emblem of remembrance in 1920, although it has been replaced by a red, white and blue ribbon on the lapel.
The Royal British Legion adopted the poppy in 1921 and, in 2010, distributed 45 million of them in England, Wales and Northern Ireland. This year, it hopes to raise £40m in donations, which will be used to assist retired or injured soldiers. According to the Royal British Legion "If you are a civilian, make sure your poppy is always close to your heart, by wearing the poppy on your left lapel, or left side of your body".
Kate Middleton and Prince William surprised commuters at a London tube station as they joined volunteers who were selling poppies.
In Scotland, about five million poppies are distributed each year by Poppyscotland, but they look slightly different. Unlike the standard two petals and a single green leaf, the Scottish ones have four petals and no leaf. There's also a financial reason for the difference, since adding a leaf would cost an extra £15,000.
Prince William has written to Fifa demanding it lifts the ban on England shirts being embroidered with poppies as Fifa decrees that shirts should not carry political, religious or commercial messages. Mr Cameron added: "The idea that wearing a poppy to remember those who have given their lives for our freedom is a political act is absurd…Wearing a poppy is an act of huge respect and national pride."
Today, in London, at a ceremony lead by the Queen, more than 10,000 military veterans and civilians marched past the Cenotaph to honour the dead soldiers of all wars. Since last year, 10 members of the UK armed forces have died during military operations.
Sky News live at the Cenotaph
Older posts about the First World War: