- Video report by ITV News Political Correspondent Paul Brand
The prime minister has told ITV News she is in the job "for the long-term" amid speculation that Boris Johnson could mount a leadership challenge.
Former foreign secretary Mr Johnson remains a threat to Theresa May after quitting the Cabinet over Brexit.
But Mrs May said she wants to deliver Brexit for the British people.
Asked by ITV News Political Correspondent Paul Brand about Mr Johnson, she said: “I was very pleased Boris was foreign secretary for the period that he was foreign secretary.”
Pressed about a potential leadership challenge, the prime minister replied: “I'm in this business for the long term because I want to deliver for the British people."
Mrs May also said that a no deal Brexit would "not be the end of the world".
Her comments come after Chancellor Philip Hammond claimed that Britain would be £80 billion worse off if no deal was reached with the European Union post-Brexit.
While Mrs May refused to be drawn on whether Mr Hammond was too negative with his no deal warning, she instead said that his figures were based on calculations which were a "work in progress in January".
Speaking in South Africa where she is part-way through a three-day trade tour, the Maidenhead MP insisted that the Government was "working for a good deal" which it had put forward in the Chequers plan, and that it was "sitting down and negotiating" with the EU's team.
Mrs May added that the plans for a no deal where a backup: "What we're doing as a Government is putting in place arrangements that ensure whatever the outcome we will make a success of leaving the European Union."
While a no deal Brexit "wouldn't be a walk in the park...it wouldn't be the end of the world", Mrs May said, but refused to be drawn on whether this could damage the UK's economy and lead to job losses.
Instead, the 61-year-old reiterated her point that the Government was working to ensure that the UK would "make a success of Brexit", creating a "future relationship which will protect jobs and livelihoods that delivers on the vote to leave the EU in a way that protects the United Kingdom and ensures there's no hard border between Northern Ireland and Ireland".
Speaking to Political Correspondent Paul Brand, Mrs May was keen to stress that there are "huge opportunities for the UK outside of the EU", highlighting Africa as one such example.
Mrs May said that trade and investment with Africa would not only create jobs in Africa, but would also create jobs in the UK and help make a success of the global Britain of the future".
Earlier on Tuesday, at a speech in Cape Town, Mrs May reasserted the UK’s shift in strategy over aid spending, encouraging private sector investment alongside efforts to alleviate extreme poverty.
Britain’s overseas aid budget - which totalled £13.9 billion in 2017 - has proven controversial among some Tory backbenchers, with successive international development secretaries vowing to use the cash to help develop trade against the backdrop of Brexit.
When Mrs May was questioned whether it was "heartless" to divert aid from some of the poorest people in the world to benefit the UK, she countered that this change in strategy was more about the "long-term interests of the people we're helping".
The prime minister continued that the UK's budget would still be used to "bring people out of poverty, to support the most vulnerable people around the world", but would also help to ensure that "economies are able to be sustainable for the future".
Mrs May was also asked her about her dancing skills which she showcased on a school visit in Cape Town on Tuesday morning.
Mrs May laughed off her smooth moves and replied that she "wasn't quite sure that my dancing would make it onto Strictly".