The family of Lady Jakobovits, 81, who is in intensive care, have asked people to recite prayers on her behalf.
Renowned for her charity work and affectionately known throughout British Jewry as Lady J, she is the widow of former Chief Rabbi Lord Jakobovits.
Prayers are being said for her in her Hebrew name of Malia bas Frummit.
Born Amelie Munk in Ansbach, Germany, she survived the war by escaping to Switzerland, and met Immanuel Jakobovits when she was 19, shortly before he became Chief Rabbi of Ireland.
The founder of the Association of United Synagogue Women, Lady Jakobovits has been a patron and supporter of numerous causes including Emunah, Jewish Care, Chai Cancer Care and Wizo.
Noted for her warmth and hospitality, her husband’s biographer Chaim Bermant said: “No - one has added more to the gaiety and colour of Anglo-Jewish life”.