In the letter, Mao request Attlee helps him to battle against Japanese troops invading China. The typed letter reads: "We believe that the British people, when they know the truth about Japanese aggression in China, will rise in support of the Chinese people, will organise practical assistance on their behalf, and will compel their own government to adopt a policy of active resistance to a danger that ultimately threatens them no less than ourselves."

Mao's letter, which has an extremely rare example of Mao's signature, was sent to Atlee through the journalist James Bertram, with a note to Attlee asking him to to "keep the enclosed letter, if only as a curiosity."

The lot, which went under the gavel at Sotheby's London premises, had an estimate of $150 000-225 000 (£100 000-150 000) and was purchased by a Chinese private collector.