They did not specify the precise cause of Sata's death.
Sata, 77, died Tuesday night with his wife and family by his side in the British capital, Zambian government spokesman Roland Msiska said, quoted by the Zambia Daily Mail.
The Zambian leader's death came after he experienced a sudden and rapid heart rate Tuesday evening.
Sata was rushed from his hotel to the King Edward VII Hospital in Westminster, but doctors could do nothing to save his life and he died three hours later.
Sata was the fifth head of state since the country's independence, the 50th anniversary of which was celebrated last week in his absence.
Since his departure from Zambia, Minister of Defence and Justice Edgar Lungu was acting president and it was still unclear who would take over after Sata's death due to a constitutional clause that could void the appointment of the current Vice President, Guy Scott.
Born in 1937 in Mpika, which was part of the British colony of Northern Rhodesia at the time, Sata worked as a police officer, railroad employee and union member before going into politics in 1963, a year before Zambia's independence.