Just a few days after the United States and Britain announced to much fanfare that they had agreed to lower some tariffs and create a $5 billion export opportunity for American beef, ethanol and other agricultural products in Britain, Brooke Rollins, the U.S. secretary of agriculture, touched down in London.

She came with a clear message for her British counterparts: The agreement last week was just the first step.

Ms. Rollins, the first member of President Trump’s cabinet to visit Britain, said she would push for more access for American products, such as pork, poultry, seafood and rice. But among her first tasks was countering the narrative in Britain, and across Europe, that American meat is substandard.

“The U.S. is open for business, and we have wholesome, quality and safe products that we want to ensure are accessible to consumers around the world and across the U.K.,” Ms. Rollins told reporters on Tuesday.

The United States is Britain’s largest single trade partner, but most of that trade is skewed toward services. Cars, fuel, pharmaceuticals and aircraft make up most of the trade in goods. Britain relies on imports for 40 percent of its food, but less than 2 percent of Britain’s imported food, including live animals, comes from the United States.