A bus full of American expats urging their countryfolk abroad to vote against Republican candidate, Donald Trump, spent Wednesday touring the British capital. Starting at University College London, the open-topped double-decker drove around landmarks handing out cookies and showing Americans how to register to vote abroad.

The campaign was organised by Avaaz, who said that of eight-million US citizens abroad, only 12% voted in the last election. They called these people "a massive untapped voting bloc" that would make up enough people to be the 13th largest state.

"Americans living abroad are the secret swing state that could tip this year's election," said Avaaz Deputy Director, Emma Ruby-Sachs. "For months, the world has sat on the sidelines, horrified by Trump's hate. Now, global citizens have a way to fight back."

The bus hit sites including the City of London and the Houses of Parliament, with passengers chanting slogans, handing out leaflets and attempting to get Americans to register to vote using Avaaz's voting tool.