A heckler has thrown a Doc Marten boot at former prime minister John Howard during a speech at Cambridge University.

Mr Howard was preparing to speak to an audience of 400 at the Cambridge Union Society on the "leadership in the new century" last Friday when a student verbally abused him and accused him of being racist.

John Howard ... had a boot thrown at him. Credit:Yuri Gripas

A Cambridge student website, The Tab, said the man began his verbal attack when Mr Howard told the audience he had been the Australian prime minister for 12 years and listed his achievements while in office.

The Tab said the man yelled: "I was ashamed to be an Australian for that entire time, racist."

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The website continued: "After this he was asked to leave the union but he refused. He took off his Doc Marten boot and attempted to throw it at the former head of government.

"Senior union members managed to intercept the boot and the man was escorted out."