Wikileaks tweeted that Assange did not voluntarily leave the embassy — writing that British authorities were”encouraged” in and immediately arrested him:
“The patience of Ecuador has reached its limitation on the behavior of Mr. Assange: He installed electronic and distortion gear not enabled. He blocked the Ecuadorian Mission’s safety cameras in London. He abused and has confronted guards. He’d obtained our Embassy’s security files without consent. He claimed to be isolated and rejected the online link offered by the embassy, and he had a cell phone with which he communicated with the outside world.”

— Sky News (@SkyNews) April 11, 2019

URGENT: political asylum has been terminated by Ecuador in violation of law. He had been arrested by the authorities inside the Ecuadorian embassy minutes. https://t.co/6Ukjh2rMKD
The Ambassador had a responsibility to execute the warrant, on behalf of Westminster Magistrates ’ Court, and invited the MPS, after the Ecuadorian government withdrawal of asylum.

“Today, I announce that the discourteous and aggressive behavior of Mr. Julian Assange, the hostile and threatening declarations of its allied organization, against Ecuador, and especially, the trangression of international treaties, have headed the situation to some point where the asylum of Mr. Assange is unsustainable and no more workable,” Moreno said.

The reason British authorities arrested him now is that he breached bail conditions in the U.K. by seeking political refuge at the Ecuadorean Embassy in 2012.

The following announcement was issued by the Metropolitan Police: