LONDON — Tens of thousands of demonstrators turned out in London alone. A “Trump Baby” balloon was launched into the sky above Parliament Square. Many people banged pots and pans and chanted slogans. Those were some of the ways people on Friday mounted protests at every stage of President Trump’s working visit to Britain.

The main protests came a day after the president’s trip was jolted by The Sun newspaper’s publication of an interview in which Mr. Trump gave a harsh assessment of Prime Minister Theresa May’s Brexit strategy and praised Boris Johnson, her Conservative Party rival, as a potentially great prime minister.

But later, Mr. Trump tried to repair the damage, calling Mrs. May “tough.”

The most anticipated installment of Britain’s “Stop Trump” protests — a giant orange balloon of Mr. Trump depicted as a pouting baby in a diaper and holding a smartphone — took flight in London earlier in the day.

As if they were waiting for a rocket launch, dozens of people — activists, tourists, children and bystanders taking time out from their commutes — gathered around the 19-foot balloon and counted down from 10 before it was released into the air.