Even on the other side of the world, Prime Minister David Cameron was unable to escape speculation about possible threats to his position from London mayor Boris Johnson.

Cameron is used to fending off rumours circulating in the UK that Johnson has his eye on the Conservative leadership and the keys to 10 Downing Street.

But he faced the same questions in Brazil, when interviewed for newspaper Folha de Sao Paulo.

Folha asked: "With the economy in crisis, we see mayor Boris Johnson, also of your party, with greater popularity than you to the point there are rumours that he might be the Conservative candidate for the next general election. Do you feel your post is threatened?"

david cameron brazil

Cameron was questioned over Boris' popularity by a Brazilian newspaper

Cameron responded: "Not at all. Boris has been a great friend of mine for a long time and a first-class mayor of London.

"We're very lucky to have many big hitters in our party, but Boris still has much work to do as mayor, and so do I as Prime Minister."

Cameron, fresh off an appearance on the Letterman show in New York, was obviously still on his guard to deal with tough questions. At least he didn't get asked about Magna Carta this time.

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  • David Cameron on "The Late Show with David Letterman" - New York

    Prime Minister David Cameron (left) talks with talk show host David Letterman on the David Letterman Show in New York, after he addressed the United Nations General Assembly.

  • David Cameron on "The Late Show with David Letterman" - New York

    Prime Minister David Cameron (left) talks with talk show host David Letterman on the David Letterman Show in New York, after he addressed the United Nations General Assembly.

  • David Cameron on "The Late Show with David Letterman" - New York

    Prime Minister David Cameron (left) looks on as talk show host David Letterman, holds up a picture of Larry the cat sitting on red carpet outside the front door of 10 Downing Street, during the David Letterman Show in New York, after he addressed the United Nations General Assembly.

  • David Cameron on "The Late Show with David Letterman" - New York

    Prime Minister David Cameron (left) talks with talk show host David Letterman on the David Letterman Show in New York, after he addressed the United Nations General Assembly.

  • David Cameron on "The Late Show with David Letterman" - New York

    Prime Minister David Cameron (left) talks with talk show host David Letterman on the David Letterman Show in New York, after he addressed the United Nations General Assembly.

  • David Cameron on "The Late Show with David Letterman" - New York

    Prime Minister David Cameron (left) talks with talk show host David Letterman on the David Letterman Show in New York, after he addressed the United Nations General Assembly.

  • David Cameron on "The Late Show with David Letterman" - New York

    Prime Minister David Cameron (left) talks with talk show host David Letterman on the David Letterman Show in New York, after he addressed the United Nations General Assembly.

  • David Cameron on "The Late Show with David Letterman" - New York

    Prime Minister David Cameron (left) talks with talk show host David Letterman on the David Letterman Show in New York, after he addressed the United Nations General Assembly.

  • Britain's Prime Minister David Cameron (left) talks with talk show host David Letterman on the David Letterman Show after he addressed the United Nations General Assembly, in New York, Wednesday, Sept. 26, 2012. (AP Photo / Stefan Rousseau/PA) UNITED KINGDOM OUT: NO SALES: NO ARCHIVE:

  • Britain's Prime Minister David Cameron (left) talks with talk show host David Letterman on the David Letterman Show after he addressed the United Nations General Assembly, in New York, Wednesday, Sept. 26, 2012. (AP Photo / Stefan Rousseau/PA) UNITED KINGDOM OUT: NO SALES: NO ARCHIVE:

  • David Cameron, David Letterman

    In this photo provided by CBS, British Prime Minister David Cameron, left, talks with host David Letterman on the set of the “Late Show with David Letterman,” Wednesday, Sept. 26, 2012 in New York. (AP Photo/CBS, John Paul Filo) MANDATORY CREDIT; NO ARCHIVE; NO SALES

  • Cameron visits US

    Prime Minister David Cameron walks through the streets of New York after addressing the UN General Assembly, in New York today.

  • Cameron visits US

    Prime Minister David Cameron walks through the streets of New York after addressing the UN General Assembly, in New York today.

  • Cameron visits US

    Prime Minister David Cameron on his way to addresses the UN General Assembly, in New York today.

  • Cameron visits US

    Prime Minister David Cameron walks through the streets of New York after addressing the UN General Assembly, in New York today.

  • Cameron visits US

    Prime Minister David Cameron walks through the streets of New York after addressing the UN General Assembly, in New York today.

  • Cameron visits US

    Prime Minister David Cameron walks through the streets of New York after addressing the UN General Assembly, in New York today.