He was relieved of five government advisory roles just hours after making his stand, and received the news from the chief whip via a phone call while having dinner with his wife.
"This is not my judgement, this is the prime minister exercising her perfectly legitimate right to get rid of opposition in any way she finds appropriate," Heseltine told the BBC.
"Sometimes in politics there are issues which transcend party politics; in the end you have to be your own person. I believe our interests are intertwined with Europe. I am not prepared to change.
"I have been hugely proud of the work I have done for David Cameron and now for this Prime Minister, and if they don't want me to go on they must sack me."
The former deputy prime minister appeared perplexed by the timing of the decision, especially given the fact he has clearly articulated his views on Britain's exit from the EU. He said:
I did write a newspaper article the other day setting out exactly what I intended to do so I think they could have told me this would be the price.
"Every Conservative prime minister I worked for has told me, including this Prime Minister before the referendum, that we were essentially seeking British self-interest in Europe."