He chose not to commemorate that day at Thiepval with the veterans of the army of which he is political master.
Before we condemn him, we should bear in mind that friends of John Redwood, his rival for the Tory leadership, are going out of their way to make us loathe Portillo. They may have fomented this fuss about his non-attendance. Nevertheless, disliking Portillo remains an important obligation for us all - his manner is disgusting, and on this occasion, as on others, he has displayed an extraordinary lack of taste.
For 1 July 1916 was both the most important day in our modern military history and among the most important in our entire history. To make matters worse for the Defence Secretary, this may be the last anniversary of that date for which we can call on living memory. Some Somme veterans are in their hundreds. They will not be with us in 10 years. The next anniversary will not really be an anniversary at all. The event will have passed fully into recorded rather than remembered history.
There is, now, some controversy about how we should judge that first day in terms of military history. For most of the 20th century - from Wilfred Owen to Rowan Atkinson's Blackadder - it has been regarded as a monumental blunder perpetrated by a callous High Command who throughout the war cared nothing for the lives of their troops. It is routinely seen as the supreme condemnation of the British class system. Working-class conscripts, lured by the call of duty and the glamour of escape, were chucked into the firing line by cruel, stupid toffs.
Revisionists now say that, though it was undoubtedly a catastrophe, it was forced upon the generals by the political and military demands of the hour. Subsequently, they learnt their lesson and won the decisive second Battle of the Somme employing considerably more humane and modern methods. And we did, after all, win the war - a victory we seem less disposed to celebrate than that of 1945.
Such a controversy has its place, not least in British self-perception. The idea that we have a criminally or comically incompetent ruling class has been a fixed and frequently debilitating aspect of our politics and our culture since the Great War. We still believe in the failings of leadership, more readily because of the slaughter at the Somme. Perhaps that belief is why I so readily dislike Portillo. But, if the generals were not really that incompetent, then our routine contempt for leaders is based upon a misreading of history, and our national habit of giving moral weight to the mannerisms of class is founded upon a lie.
But that issue becomes almost insignificant, a local matter, when set against the elemental spectacle of mechanised, futile slaughter provided by that first day of battle. It is said that more died on that first day of the Somme than had died in the whole previous century of conflicts in Europe. A hundred years of relative peace had led to this. Human progress would always, thereafter, seem a thin, vain, unconvincing faith. For this was a moment that seemed to come from beyond history, a timeless statement of the perpetual possibility of absolute failure.
In many ways, as the historian and critic Paul Fussel has pointed out, it was an image that created the modern sensibility. The blood and mud of the trenches when set against the mannered civilisation of Edwardian England gave birth to a peculiarly modern form of irony based upon the awareness of the contingent, organic mess that lies beneath the enforced order of society. Order itself became a kind of joke, a desperate, doomed attempt to avoid the abyss.
And it gave birth to the modern sense of the human reality of the masses. As the best poems of the time prove, the patrician officers suddenly saw in those massacred brigades of chums and pals not undifferentiated cannon fodder but men like themselves. Wilfred Owen's clay that grew tall formed not the sensitive, cultivated, suffering poet, but Everyman.
This was a realisation whose importance can hardly be overstated. Leaving aside salvation and the immortal soul, the essential secular message of Christianity is: ordinary people have feelings too. It is a radical statement of the irreducibility and commonality of human experience. It took a while to sink in - about 1,880 years, in fact, the length of time between the Sermon on the Mount and 1 July 1916. But when it did, the shock brought one civilisation to an end and ushered in a modern world in which there can be no ultimate legitimacy but that of mass approval, in which some form of equality, however attenuated, is part of everybody's political predisposition.
This, along with the technology that made mass killing possible, changed the complexion of war itself - though oddly, for the worse. Once the masses acquired a voice to which their leaders had to listen, they also became a legitimate target. The bombing of civilian populations in the Second World War signalled the realisation that armies alone were not the point, people were - both because of what they did and what they felt. So 1914- 18 had not been the war to end wars, but rather the war that broadened the definition of conflict to include us all.
All of which is to say that Portillo should have been there on Monday. This commemoration, for all its vast significance, was still a military event; he was the one politician who had to attend. But, in truth, we should all have been there. Those ancient veterans witnessed a terrible battle, one of the worst in history, but they were also there at the awful birth pangs of the contemporary world. Soon they will be gone and we shall begin, as we always do, to forget.