Hari and other parts with sources not cited 

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The following was deleted:

According to Hari, in November 2001, Steyn circulated a series of conspiracy theories that a huge number of Muslims in New York City had been forwarned of the terror attacks. A Muslim student at a Brooklyn high school, he claims, said to his teacher on 6 September 2001: "See those two buildings? They won't be standing there next week." 

On 10 September 2001, Steyn further claimed, "a sixth-grade 
[NOTE: HOW COULD STEYN HAVE CLAIMED THIS ON 10 SEPT 2001? THIS STATEMENT MUST BE TOTALLY FALSE.]
student of Middle Eastern origin at a Jersey City school warned his teacher to stay away from Lower Manhattan because "something bad was going to happen". Teachers at schools within sight of the World Trade Center in New York reported that, as the towers burned, many Muslim students were taking pictures: it seemed odd that so many of them happened to have brought their cameras to school on that particular day."

Hari commented: 

"Almost no evidence has been offered in support of [this] claim. Steyn cites only the "evidence" of a disgraced and sacked journalist on a suburban New York paper, and even that is for just one of several "facts" that he cites. [...] Steyn seems to believe seriously that many American Muslims knew about the plan and did not warn anybody - not even the 300-plus Muslims who were murdered in the attack... "

Steyn himself wrote:

In The River War (1899), Winston Churchill's account of the Sudanese campaign, there's a memorable passage which I reproduce here while I'm still able to: 
"How dreadful are the curses which Mohammedanism lays on its votaries! Besides the fanatical frenzy, which is as dangerous in a man as hydrophobia in a dog, there is this fearful fatalistic apathy. Improvident habits, slovenly systems of agriculture, sluggish methods of commerce, and insecurity of property exist wherever the followers of the Prophet rule or live. A degraded sensualism deprives this life of its grace and refinement; the next of its dignity and sanctity. The fact that in Mohammedan law every woman must belong to some man as his absolute property - either as a child, a wife, or a concubine - must delay the final extinction of slavery until the faith of Islam has ceased to be a great power among men.

"Individual Moslems may show splendid qualities. Thousands become the brave and loyal soldiers of the Queen: all know how to die. But the influence of the religion paralyses the social development of those who follow it. No stronger retrograde force exists in the world. Far from being moribund, Mohammedanism is a militant and proselytising faith. It has already spread throughout Central Africa, raising fearless warriors at every step; and were it not that Christianity is sheltered in the strong arms of science - the science against which it had vainly struggled - the civilisation of modern Europe might fall, as fell the civilisation of ancient Rome."

Is that grossly offensive to Muslims? Almost certainly. Is it also a rather shrewd and pertinent analysis by one of Britain's most eminent leaders? I think so.