Curses. Eighteen months ago I had to go to London and pay a fee to watch this, on VHS in the basement of the British Film Institute. Now you can watch it in the comfort of your own or somebody else's home:
http://player.bfi.org.uk/film/watch-somme-1927/
Tank business starts at about 1h15min.
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"Sometimes things that are not true are included in Wikipedia. While at first glance that may appear like a very great problem for Wikipedia, in reality is it not. In fact, it's a good thing." - Wikipedia.