And on Remembrance Day, the same flowers will be found in wreaths laid at memorial sites across the country.
But what exactly is the significance of the flower, what do its alternative colours mean, and why is it such a divisive topic?
Here’s everything you need to know.
When should I wear my poppy?
In the UK, red poppies become widespread from late October until mid-November every year.
If you’re looking for a more specific date, it's often suggested that poppies are worn for the two weeks up to and including 11 November.
That would mean wearing a poppy – on the left lapel, or as near the heart as possible – from 28 October onwards.
Why are red poppies worn?
The tradition of wearing red poppies on Remembrance Day has its origins in Canadian poet John McCrae's 1915 piece, In Flanders Fields.
In it, the Lieutenant Colonel describes the poppies growing between the crosses marking the graves of fallen soldiers, writing that, "In Flanders fields the poppies blow, between the crosses, row on row."
Following the first World War, American academic and humanitarian Moina Michael then worked to have the poppy recognised as the official symbol of Remembrance in the US, working with those in the UK, Australia and Canada to do the same.
The charitable connotation of the poppy came a few years later, when a French woman named Anna Guérin met with the Royal British Legion in 1921, a charity which provides support to British veterans and their families.
She wanted the charity to take on the poppy as their symbol and they agreed, purchasing nine million poppies and selling them to raise over £100,000.
To date, the Royal British Legion’s annual Poppy Appeal has brought in over £3 billion – that's more than a pound-per-second since the war ended.
Why do some people choose not to wear a poppy?
The Royal British Legion has always maintained that the red poppy “is a symbol of peace inclusive of all regardless of race, belief, origin, or sexual/gender identity… and is above partisan and political interpretation.”
But many do not believe this to be the case, and with the poppy’s specific ties to the military, it can be seen by many as a symbol that glamorises war rather than commemorating the dead.
There has been growing controversy over the Poppy Appeal in recent years too, with some – including British Army veterans – arguing the Appeal has become excessive, and is being used to drum up support for British military activities.
Many public figures also complain that poppy wearing has become somewhat compulsory for them; the absence of a poppy is interpreted as an absence of concern for the war dead – an unpatriotic act of treachery.
It’s also been suggested that politicians have exploited the poppy to justify further wars, sending more young troops into unnecessary combat while they proudly display their bright red flowers.
Why do some people wear white poppies?
In recent years, white poppies on Remembrance Day have become much more commonplace, as a way to mourn the dead while emphasising a pacifistic, “never-again” message.
But the white poppy alternative was actually launched in 1933, as the red poppy’s message was feared to have been lost amidst militaristic commemorations.
In modern times, white poppies have been distributed by the UK's pacifist charity, the Peace Pledge Union. They have proven especially popular recently – around 100,000 are sold each year.
But as is the case with such sensitive subject material, even white poppies have drawn their own share of criticism, with traditionalists claiming that anything but a red poppy undermines the impact of Remembrance Day.
What other colours of poppy do people wear?
Black poppies have been used to specifically commemorate the sacrifices of black, African and Caribbean people, which are commonly overlooked.
Previously, there were also purple poppies, supplied by Animal Aid in remembrance of the animal lives lost in war, but they were discontinued after the charity concluded that their message was becoming distorted.
While they do not supply them, the Royal British Legion has also made clear that it fully supports the wearing of all colours of poppy.