The Daily Telegraph said Stewart was denied a visa to enter the country by the U.K. Border Agency because of her conviction for obstructing justice.
Stewart served five months in prison in 2004 for lying to federal agents investigating the sale of company shares shortly before they fell sharply in value.
The 66-year-old lifestyle expert, cook, designer and publisher was planning to travel to England within the next few days to speak at the Royal Academy and meet with several people in the fashion and leisure industries, the newspaper said.
"Martha loves England and hopes this can be resolved and that she will be able to visit soon," Stewart's representative told the Telegraph.
Although the agency declined to comment on individual cases, a spokesman for the division told the newspaper: "We continue to oppose the entry to the U.K. of individuals where we believe their presence in the United Kingdom is not conducive to the public good or where they have been found guilty of serious criminal offenses abroad."