Big B, who also read out an excerpt from Gandhi's "The World of Tomorrow", shared his excitement on social media.
"A historic moment and a historic presence. I am honoured and humbled. I am so touched and honoured to have been given this pride of place at this most prestigious occasion," Amitabh wrote on his official blog srbachchan.tumblr.com.
He added on Twitter: "At the unveiling, the respect and dignity given... So humbling. David Cameron, Arun Jaitley, Gopal Gandhi and self on stage! Honour."
British sculptor Philip Jackson created the statue, which was unveiled on Saturday.
The 72-year-old Amitabh was joined by British Prime Minister David Cameron, Indian Finance Minister Arun Jaitley and Gopalkrishna Gandhi, a grandson of Mahatma Gandhi.
Amitabh also posted a series of photographs from his visit to London.