Born Marian Bragg in South London, Jeffares was a relation of William Henry Bragg and Sir Lawrence Bragg (co-winners of the 1915 Nobel Prize for Physics for their work on x-rays). She studied at Blackheath Art School and for five years at the Slade School of Art in London. She also studied design at Chelsea Polytechnic, and in 1939 took a degree in art history at the Courtauld Institute, studying under Sir Anthony Blunt.

Prior to WWII she married Ernest Holfenth, with whom she had a child, but the marriage barely outlasted the war. During the intervening years she worked at the War Office in London and taught art in Manchester.

Her second marriage was to George Jeffares, an Irishman who lectured in langua...