The teenager made a major breakthrough at the Australian swimming trials when she finished second in the 100 metres breaststroke behind Olympic champion Leisel Jones and ahead of Sarah Katsoulis, a World Championship medallist.

Her grandfather, who was Australia's Prime Minister between 1975 and 1983, was in the stands in Sydney to watch Marshall book her place in the team for Games.

Fraser said: "She's persistent and she trains enormously hard and she's very focused.

"She's totally committed to swimming.

"She had a lot to learn but she's so much more composed now than she was a couple of years ago."

Marshall had narrowly missed out on Australia's team for the Olympics in Beijing two years ago when she finished fourth in the trials.

She said: "I've been ranked second going into the final before and stuffed it up, so I just wanted to swim my own race."

Gough Whitlam, who Fraser succeeded as Prime Minister, was also interested in how Marshall did.

His wife, Margaret Dovey, had competed for Australia in the then-Empire Games in Sydney in 1938 and Marshall had won the Margaret Dovey (Whitlam) trophy for the best sportswoman at the SCEGGS Darlinghurst School for the past three years.

Fraser said: "I saw Gough about two weeks ago and he was well aware that Sam was in this meet.

"He asked how the Margaret Whitlam trophy winner was going."