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

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."

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."

Julien Domercq, president of the Cambridge Union Society, said the union is a ‘‘forum for open discussion and debate’’, and ‘‘offers members a safe environment in which to express their opinions freely’’.

‘‘We cannot condone this kind of behaviour, and hope that our members will not be discouraged from engaging in reasoned dialogue in future events.’’

Mr Domerq said the CUS had ‘‘robust procedures in place, which are implemented by experienced professionals, to ensure that all our high profile guests are safe when they speak at the union.’’

A CUS press officer told The Age an independent witness described the attacker as ‘‘a total idiot - he threw it at the start of the talk, before even hearing what Mr Howard had to say. His throw was pathetic.’’

It is not the first time Cambridge has hit the headlines over shoe-throwing. In February Cambridge student Martin Jahnke threw a shoe at the visiting Chinese Premier, Wen Jiabao.

Local police were unable to confirm if any action had been taken against Mr Howard’s assailant.

The Age