“It is an extraordinary event, a monstrous event, an event which stands in singular and sinister isolation.”
Speech in the House of Commons, July 8, 1920 "Amritsar" http://lachlan.bluehaze.com.au/churchill/am-text.htm ; at the time, Churchill was serving as Secretary of State for War under Prime Minister David Lloyd George
Early career years (1898–1929)
Context: However we may dwell upon the difficulties of General Dyer during the Amritsar riots, upon the anxious and critical situation in the Punjab, upon the danger to Europeans throughout that province, … one tremendous fact stands out – I mean the slaughter of nearly 400 persons and the wounding of probably three to four times as many, at the Jallian Wallah Bagh on 13th April. That is an episode which appears to me to be without precedent or parallel in the modern history of the British Empire. … It is an extraordinary event, a monstrous event, an event which stands in singular and sinister isolation.
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Winston S. Churchill 601
Prime Minister of the United Kingdom 1874–1965Related quotes

The Need for Transcendence in the Postmodern World (1994)
Context: Until recently, it might have seemed that we were an unhappy bit of mildew on a heavenly body whirling in space among many that have no mildew on them at all. this was something that classical science could explain. Yet, the moment it begins to appear that we are deeply connected to the entire universe, science reaches the outer limits of its powers. Because it is founded on the search for universal laws, it cannot deal with singularity, that is, with uniqueness. The universe is a unique event and a unique story, and so far we are the unique point of that story. But unique events and stories are the domain of poetry, not science. With the formulation of the Anthropic Cosmological Principle, science has found itself on the border between formula and story, between science and myth. In that, however, science has paradoxically returned, in a roundabout way, to man, and offers him — in new clothing — his lost integrity. It does so by anchoring him once more in the cosmos.

Al - Jazeera Broadcast Tape - On 9/11 and the American reaction http://www.youtube.com/watch?v=dls5JTD-uG0 (The date of this tape is not provided, though it seems to be 2002 or 2003, but could be as early as October 2001.)
2000s

Session 729, Page 520
The “Unknown” Reality: Volume Two, (1979)

Response to a journalist when asked what is most likely to blow governments off course.
The quote is also given as "Events, my dear boy, events", with the word "my", but it may never have been uttered at all.
[What they didn't say: a book of misquotations, Knowles, Elizabeth M., Oxford University Press, 2006, vi, 33]
Disputed

The Phoenix, a Linguistic Phenomenon, ch. 1
Fragments of a Poetics of Fire (1988)

Source: Outlines of a Philosophy of Art, 1925, p. 41

Source: The Image: A Guide to Pseudo-Events in America (1961), p. 31.