february £20 ronald coyne cambridge university conservatives pembroke college
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The student, understood to be Ronald Coyne from Pembroke College, was filmed in Cambridge on 2 February.
The Tab reported the film showed the student wearing white tie attempting to set fire to the cash, before the camera panned to a homeless man.
The allegations are being investigated by university chiefs.
In a statement, a spokeswoman said the university was "aware of an incident" but could not comment further while the disciplinary process was under way.
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Images from a video taken in the early hours of last Thursday were sent to student newspaper The Tab.
Mr Coyne was the communications officer for Cambridge University Conservative Association (CUCA), a position he was dismissed from last week.
A statement posted on the group's website, said the "committee was made aware of the private behaviour of an individual member which we considered to be abhorrent and repugnant".
"We took immediate action to revoke his membership and expelled him from the association."
His actions were not representative of the group, they said, and added: "We wish to totally disassociate ourselves from the individual and his behaviour."
Cambridgeshire Police said they had not received any reports or complaints, adding although it was illegal to deface a bank note, it was not a crime to burn one.