In 1974, when Labour returned to power, Hart was nearly passed over for a ministerial post due to her and her husband's connections to communism.

Nonetheless, her opposition to British membership of the European Economic Community (EEC), which she believed would have a negative impact on British aid to the third world, ensured that she would be a casualty of Wilson's purge of the "anti-marketeers" following the outcome of the referendum on EEC membership in 1975.

[4] Later, following her return as Minister of Overseas Development in 1977, Hart developed a plan to redistribute British aid to prioritise the poorest countries, but it conflicted with diplomatic and trade priorities and was thwarted by the Conservative victory at the 1979 general election.

Within the Labour Party she was a member of the National Executive Committee from 1969 to 1983, serving as vice-chairman in 1980–81, and as chairman in 1981–82.

[7] She met her husband, Dr Anthony Bernard Hart (always known as Tony), at an Association of Scientific Workers meeting.

He was also politically active, but when they were both selected as candidates for the Labour party in 1959, he withdrew his candidacy to support her campaign.

When Hart was appointed Minister of State for Commonwealth Affairs in 1966, her mother-in-law moved in to help with the children.

[2] She died of bone cancer at the Queen Mary's Hospital, Roehampton, London, in 1991, aged 67.