As punishment for their actions, the trio are ordered by the headmaster to clean out a large storeroom beneath the main school hall.

Led by a visiting general who had been giving a speech, the staff, students, and parents break open the Combined Cadet Force armoury and begin firing back.

The film's surrealist sequences have been compared to Jean Vigo's French classic Zéro de conduite (1933).

"[4] David Sherwin's original title for the screenplay was Crusaders, during the writing of which he drew heavily from his experiences at Tonbridge School in Kent.

[5] The school used for the early filming on location was Anderson's alma mater, Cheltenham College, Gloucestershire, but this was not made public at the time under the agreement needed to shoot there.

Aldenham School in Elstree, Hertfordshire, was used for later scenes filmed after previous summer commitments prevented further shooting at Cheltenham.

The outside shots of the school including the final showdown on the roof were filmed at Cheltenham College after term ended.

The Speech Day interior was filmed inside St John's Church on Albion Street, Cheltenham.

In the audio commentary to the 2007 DVD release, Malcolm McDowell confirmed that lighting the chapel scenes for colour filming would have taken much longer than for black and white.

[9] Music featured in the film includes the 'Sanctus', from the Missa Luba, a rendering of the Roman Latin mass sung to African beat by a Congolese choir.

[10] Time Out wrote: "A modern classic in which Anderson minutely captures both the particular ethos of a public school and the general flavour of any structured community, thus achieving a clear allegorical force without sacrificing a whit of his exploration of an essentially British institution.

The impeccable logic of the conclusion is in no way diminished by having been lifted from Vigo's Zéro de Conduite [1933], made thirty-five years earlier.

"[11] Variety wrote: "Timely and timeless, this is a punchy, poetic pic that delves into the epic theme of youthful revolt.

...The script has the expert blend of heightened reality and lyricism enforced by the brilliant direction and the playing of a cast of unknowns.

"[12] The Radio Times Guide to Films gave the film 4/5 stars, writing: "With its surrealistic elements, it was something of a departure for This Sporting Life [1963] director Lindsay Anderson, but he succeeds in both capturing the atmosphere and absurdities of public school life and investing the satire with plenty of venom.

"[13] Leslie Halliwell, dissenting from the general praise for the film, wrote that "Allegorical treatment of school life with much fashionable emphasis on obscure narrative, clever cutting, variety of pace, even an unaccountable changing from colour to monochrome and vice versa.

Intelligence is clearly at work, but it seems to have suffered from undigested gobs of Pinter, and the film as a whole makes no discernible point.

In 2017 a poll of 150 actors, directors, writers, producers and critics for Time Out magazine ranked it the 9th best British film ever.

[17] McDowell's performance in If.... caught the attention of Stanley Kubrick, who subsequently cast him in his 1971 film adaptation of Anthony Burgess's A Clockwork Orange.