McCrae had been tending the wounded for 17 of the most terrible fighting days that any army has seen. He described it as "seventeen days of Hades. At the end of the first day, if anyone had told us we would have to spend seventeen days there, we would have folded our hands and said it could not be done." But it was done and, on the last of those days, having seen his best friend killed by a shell burst, and acted as chaplain to bury him, he sat down, and in 15 minutes scrawled what he thought was a verse too sentimental to survive: "In Flanders fields the poppies grow/Between the crosses row on row..."

Sentimental it is, but it contains the germ of an idea that has transcended generations, and survived for close on 90 years - it is that, exposed to death and suffering on a scale unimaginable to the rest of us, the only comfort remaining to the fighting soldier is that his sacrifice shall be remembered; that it means something, not just to his comrades and his family, but to those who, thanks to him, will have the luxury of life and the freedom to enjoy it. So when, last week, Snow announced that he was refusing to wear a poppy on his lapel while he was on air, he was choosing to sever that link. He was turning his back on the tradition of honouring, publicly, the memory of the one million Britons who were killed or went missing in "the war to end all wars".

His argument, naturally, was balanced and reasonable. He described the convention whereby broadcasters and other public figures are expected to wear poppies in the run-up to Armistice Day as "poppy fascism," and said he refused to be pigeon-holed by any symbol, however worthy. He had rejected requests to wear breast cancer ribbons or RNIB badges, so why should he make an exception for the poppy? It was one thing, he said, to don the flamboyant ties which are his personal trademark, quite another to subscribe to a public gesture which might compromise his role as an objective journalist. "I do not believe in wearing anything that represents any kind of statement," he said, adding: "In the end, there really must be more important things in life than whether a news presenter wears symbols on his lapels."

He betrays himself with that last remark. If it is so unimportant, why post his views on the internet? And if not, then what is he really saying? That remembering the dead of all our wars is simply another ritual, no more nor less significant than supporting a cancer charity or giving money to the blind? That proclaiming his journalistic integrity is more important than honouring those who paid for his freedom with their lives? That requiring a TV news presenter to wear a poppy is tantamount to the fascism against which two world wars were fought?

The argument is absurd. But it takes place at a critical time, when symbols of all kinds are subject to intense scrutiny. Snow himself questions the right of another presenter, Fiona Bruce of the BBC, to wear a piece of jewellery shaped like a crucifix. A fierce debate is taking place about the right of Muslim women to wear the veil in schools, or whenever they are engaged in human contact with others. Even the red poppy itself has been criticised as indicating an attitude which encourages militarism and therefore the continuation of war rather than standing up for peace; thousands of people who choose not to wear it do so because they feel they are aligning themselves with an Establishment which has shown itself willing to wage a succession of wars, from the Gulf to Afghanistan, and which manufactures weapons of mass destruction. It is for this reason that another symbol is increasingly seen: the white poppy, first introduced in the 1930s as a peace gesture, now more militantly displayed as a statement of the anti-war protester. It was to be seen last week on the lapels of left-wing MSPs, notably amongst the thinning ranks of the Scottish Socialist Party.

They would argue that theirs is the moral high ground; that they are echoing Albert Einstein when he said: "Nothing will end war unless the people themselves refuse to go to war", or John Lennon, who famously proclaimed: "If everyone demanded peace instead of another television set then there'd be peace."

But this, surely, is the ultimate betrayal of those who died in the mud of Flanders, and who continue to die on our behalf in Iraq and Afghanistan.

It is the red poppy, not the white, which is their flower, their symbol, and the ultimate proclamation that war is hell. It was they who asked us to wear it, and by doing so we are giving thanks for a sacrifice which can never be repaid, and reminding ourselves at the same time of the human cost of war. We align ourselves, not only with the poignancy of John McCrae, but also with the bitterness of another war poet, Wilfred Owen, who forced us to confront the true horror of war and the hypocrisy of those who send young soldiers to die for the wrong reasons. He pictures the death of a fallen comrade, exposed to gas and dying in agony:

If in some smothering dreams you too could pace/Behind the wagon that we flung him in,/And watch the white eyes writhing in his face,/His hanging face, like a devil's sick of sin;/If you could hear, at every jolt, the blood,/Come gargling from the froth-corrupted lungs/... My friend, you would not tell with such high zest/To children ardent for some desperate glory,/The old Lie; Dulce et Decorum est/Pro patria mori.

That surely is what the red poppy reminds us of, whether on the streets of the nation today, or in the comfort of a television studio. It is there, for all time, lest we forget.