Biggest British Documentary
It is difficult to say what the biggest British documentary is, as opinions may vary on what the "biggest" documentary is. There are many British documentaries that have been critically acclaimed and/or commercially successful, but it's hard to pick one that could be considered the "biggest". Some notable British documentaries include:
"Planet Earth": A 2006 nature documentary series that was produced by the BBC Natural History Unit, which explores the diversity of life on Earth. It was narrated by Sir David Attenborough, and it broke ratings records in the UK, as well as around the world, where it was distributed to more than 130 countries
"Blue Planet": A 2001 nature documentary series also produced by BBC, and narrated by Sir David Attenborough, which explores the Earth's oceans and marine life. It also garnered significant success.
"Senna": A 2010 documentary about the life and career of Brazilian Formula One racing driver Ayrton Senna, directed by Asif Kapadia. It won numerous awards, including the World Cinema Audience Award at the Sundance Film Festival and the BAFTA for Best Documentary.
"Amy": A 2015 documentary film directed by Asif Kapadia and produced by James Gay-Rees, that tells the life story of British singer and songwriter Amy Winehouse, it was the recipient of several awards and nominations, including the BAFTA award for Best Documentary
"The Act of Killing": A 2012 documentary film directed by Joshua Oppenheimer and produced by Signe Byrge Sørensen, it tells the story of the Indonesian mass killings of 1965–66, using the cinematic devices of the surreal and the fantastical, and it won numerous awards.
These are just a few examples, and there are many other notable British documentaries that have been critically acclaimed and/or commercially successful.