London: British Prime Minister Theresa May declined to rule out firing outspoken Foreign Secretary Boris Johnson as she said was in control of her country's strategy for Brexit.

Asked directly by Sky News whether Johnson should be ousted for freelancing on how Britain should leave the European Union, Mrs May ducked the question and gave the tepid endorsement that he was "doing good work" as her top diplomat.

British Prime Minister Theresa May, left, speaks at a UN side panel next to UN Secretary General Antonio Guterres in New York on Tuesday. Credit:AP

"Boris and others" are "all very clear about the destination we have as a country and that is getting that deep and special relationship with the EU when we leave," Mrs May said in New York, where she and Mr Johnson are attending meetings of the United Nations.

Mrs May spoke as media reports gave conflicting reports over Mr Johnson's future days after he released a 4200-word opus on his vision for Brexit that took a harder line than others in the government.