The man, who is barefoot and holds a Palestine flag, has been spoken to by negotiators several times but at 10.30pm had not yet agreed to come down.
A 29-year-old man has been charged after climbing onto the clock tower of Big Ben, Metropolitan Police said. Daniel Day, of Palmerston Road, Westcliff-on-Sea, Essex, has been charged with intentionally or recklessly causing a public nuisance and trespassing on a protected site.
The United Kingdom-based activist group Palestine Action said it "rejects Donald Trump's treatment of Gaza as though it were his property to dispose of as he likes."
A barefoot man who scaled Big Ben's tower with a Palestine flag has been on the building for more than seven hours.
Activists targeted a Trump-owned golf course in Scotland early on Saturday morning, painting "Gaza Is Not For Sale" on the lawn