Baron Israel Moses Sieff

British industrialist and Zionist Baron Israel Moses Sieff was born in Manchester, where his father, a migrant from Lithuania, founded a prosperous business. He and his brothers-in-law, Simon Marks and Harry Sacher, were closely associated in their devotion to Zionism, as well as in their commercial career. Sieff 's wife, Rebecca Sieff, was among the founders of WIZO and continued her active participation in that organization.

It was in 1913 that Sieff, along with Marks, came to know Chaim Weizmann, who was at that time a lecturer in Manchester University. From then on until Weizmann's death, the three brothers-in-law were among his closest friends and collaborators, notably in the critical labors which led up to the issue of the Balfour Declaration. Under their leadership Manchester became arguably the major center of British Zionism.

Sieff was one of the founders of and a regular contributor to the fortnightly review Palestine, which played its part in educating public opinion in England in favor of Zionism. In 1918, when the Zionist Commission headed by Weizmann went to Palestine to prepare the ground for the implementation of the Declaration, Sieff acted as its secretary.

He joined Marks when the main offices of their firm, Marks and Spencer Limited, were transferred to London, and played a notable part in its development. He was the vice chairman and joint managing director of the company and in 1967 became its president. Not restricting his activities to Zionist matters, Sieff was the founder of Political and Economic Planning (PEP), an organization of internationally recognized authority, and was its chairman (1931–39), vice chairman (1939–64), and president from 1966. He was also a vice chairman of the Royal Anthropological Institute.

A noted philanthropist, Sieff, together with other members of the family, founded the Daniel Sieff Research Institute at Reḥovot, from which the Weizmann Institute of Science developed. His Zionist and Jewish activities were marked by his honorary presidency of the Zionist Federation of Great Britain and Ireland and of that body's Educational Trust, his chairmanship and vice presidency of the Joint Palestine Appeal, and his chairmanship of Carmel College. He was made a life peer in 1966.

His younger son MARCUS JOSEPH SIEFF, BARON SIEFF OF BRIMPTON (1913–2001), who was educated at Manchester Grammar School and Cambridge, joined the family firm in 1945, became a director in 1954, and, after 1967, was managing director and chairman. He expanded the range of Marks & Spencer to include the sale of food. Like other members of his family he was a notable contributor to Jewish and Zionist causes. Sieff wrote an autobiography, Don't Ask the Price (1986). After his retirement the firm experienced increasing difficulties, and ceased to be a family or, indeed, a Jewish firm. Sieff was knighted in 1971 and received a life peerage in 1980.

In 1970, his memoirs (The Memoirs of Israel Sieff) were published.