LONDON — A measure of the strangeness of the times in Brexit Britain is that one can buy T-shirts bearing the face of John Bercow, the speaker of the House of Commons, in the stylized stencil preferred by street artists and skateboarders, with the word ORDER.

“He is spitting the best sassy statements in that charming accent,” said Kaarlo Junkkari, a 19-year-old Finnish man who sells the T-shirts online. He said he had become fascinated with Mr. Bercow, whose prolix verbal style and braying cries of “order, order!” have made him one of Brexit’s “spicy memes.”

But this enthusiasm is not universal in Britain, especially on Tuesday, after Mr. Bercow startled the country by blocking Prime Minister Theresa May’s plan to push her withdrawal agreement through Parliament before a trip on Thursday to Brussels. He announced that he would not allow a third vote on her plan for Brexit, as the departure from the European Union is known, unless the plan differed from the one rejected last week.

This ruling — based on an obscure precedent from 1604 — has made Mr. Bercow, a wonky arbiter of parliamentary procedure, one of the most admired and hated men in the country.