James O'Brien, from Co. Mayo, was selling Trump toilet paper at Oxford Circus and was attracting amused passers-by.
"We thought it'd be fun," he said.
Getting the attention of potential buyers, he noted: "The most satisfaction you can have in a toilet, kids."
A percentage of the money raised from the toilet rolls is going towards mental health awareness.
Tens of thousands of protesters have swarmed the streets of central London to protest during Donald Trump's first visit to the UK as US president.
Organisers of the Together Against Trump mass demonstration claimed they had been told by police that more than 100,000 protesters had joined the march by mid-afternoon.