Rotblat returned to Britain to become senior lecturer and acting director of research in nuclear physics at the University of Liverpool. He was naturalised as a British subject on 8 January 1946. Most of his family had survived the war. With the help of a Polish man, his brother-in-law Mieczysław (Mietek) Pokorny had created false Polish Catholic identities for Rotblat's sister Ewa and niece Halina. Ewa, taking advantage of the fact that she was an ash blonde who, like Rotblat, spoke fluent Polish as well as Yiddish, smuggled the rest of the family out of the Warsaw Ghetto. Mietek, Rotblat's brother Mordecai (Michael) and Michael's wife Manya, Rotblat's mother Scheindel, and two Russian soldiers lived in a concealed bunker underneath a house near Otwock, in which Ewa and Halina lived with a Polish family. Displays of Polish anti-Semitism that she witnessed during the Warsaw Ghetto uprising embittered Ewa towards Poland, and she petitioned Rotblat to help the family emigrate to England. He therefore now accepted Chadwick's offer of British citizenship so he could help them escape from Poland. They lived with him in London for some time before becoming established. Halina would go on to graduate from Somerville College, Oxford, and University College London, and become an editor of the Dictionary of National Biography.