“I am voting for Hillary because she is a woman,” said Mary, as she opened her exhibition of pioneering Sixties girl group The Supremes’ costumes at London’s Victoria & Albert Museum.

“The world needs healing and that is a job for women. Of course, it’s OK with me if Obama wins. Having a black president will improve things for blacks in the US. Even in the White House he won’t forget that he is black; you can’t forget something like that.”

The show contains 50 of the group’s show-stopping dresses, including a pink beaded outfit Mary, now a youthful-looking 64, wore to meet the Queen Mother at a Royal Command Performance in 1968.

The Supremes caused controversy at that event by calling for increased racial tolerance in the US.

“Our success was part of the struggle for civil rights in America,” said Mary of the group, which carried on for seven years after Diana Ross departed for solo stardom in 1970.

“Diana is like a sister to me,” she said of their relationship now, before she added tellingly, “although we don’t talk much.”