The relationship between the Prime Minister of the United Kingdom and the President of the United States is typically characterized by cooperation and transparency, especially regarding matters of diplomacy, security, and trade. However, like any leaders, they may have sensitive information related to national security, intelligence, or domestic affairs that they choose not to disclose to foreign leaders to protect their country's interests.
Ultimately, whether they have something to hide would depend on the specific circumstances and context of their discussions. Transparency is vital for international relations, but leaders must also balance that with the need to protect sensitive information.