I have used a range of sources for quotations and biographical information about Anderson, and about the making of these films. These include:
Anderson’s Diaries, edited by Paul Sutton (London: Methuen, 2004) – these include the ‘self-interview’ produced for the release of If….
Never Apologise: The Collected Writings, edited by Paul Ryan (London: Plexus, 2004), includes several key examples of Anderson’s film and theatre criticism, including the essay ‘Critical Betrayal’ on academic Film Studies. The book has several pieces on If…., a ‘commentary’ and an interview on O Lucky Man! and a further ‘commentary’ on Britannia Hospital.
Mainly about Lindsay Anderson: A Memoir by Gavin Lambert (London: Faber and Faber, 2000) has a section on If….
I have also used a 1989 interview with Anderson published in Wheeler Winston Dixon’s collection Re-Viewing British Cinema, 1900-1992: Essays and Interviews (Albany: SUNY Press, 1994).
Malcolm MacDowell’s filmed one-man show Never Apologise (Double M Productions, 2008) is a typical actorly memoir: it can be seen on YouTube at https://www.youtube.com/watch?v=9Un0htx29R0
There is also an edition of the BBC/Open University programme Cast and Crew with a studio discussion including key members of the crew of If…, as well as MacDowell (on film), made in 2005: https://www.youtube.com/watch?v=zcbvYmyh9JA. From this I have drawn some quotes from Ian Rakoff and David Sherwin.
In terms of academic commentary, the only full-length book is Erik Hedling’s Lindsay Anderson: Maverick Film-Maker (London: Cassell, 1998). This covers all the films, although Hedling falls over himself to dismiss any criticisms of Anderson.
There are brief discussions of Anderson’s films in surveys of British cinema, such as Jim Leach’s British Film (Cambridge: Cambridge University Press, 2004) and Robert Murphy’s edited collection The British Cinema Book (third edition, Basingstoke: Palgrave MacMillan, 2009) – although he is notable for his absence from many key texts.
Specifically on If…, there are two short books: Mark Sinker’s study in the British Film Institute’s Film Classics series (London: BFI Publishing, 2004) and Paul Sutton’s in the Turner Film Classics series (London: I.B. Tauris, 2005). Sinker’s style is somewhat pretentious, but his book is rather more critical than Sutton’s.
In my view, the most balanced critical analysis remains Jeffrey Richards’s chapter ‘The revolt of the young: If…’, in Anthony Aldgate and Jeffrey Richards Best of British: Cinema and Society from 1930 to the Present (new edition, London: I.B. Tauris, 1999).
Contemporary reviews of the film can be found online, notably in a slide show on IMDB. Gavin Lambert’s Guardian article is at: https://www.theguardian.com/film/2002/feb/15/artsfeatures. Garry Mulholland’s Stranded at the Drive-In is published by Orion Books (London, 2011).
Colin MacCabe’s critique of Anderson can be found in his article ‘Realism in the cinema: notes on some Brechtian theses’, Screen 15(2): 7-27 (1974).
On Britannia Hospital, I have also used this account of the critical response to the film: ‘In Search of an Audience: Lindsay Anderson’s Britannia Hospital’ by Kathryn Mackenzie and Karl Magee in Participations 6(2), 2009, online at http://www.participations.org/Volume%206/Issue%202/special/mackenzie.htm