LONDON (Reuters) - Activists urging American expats in Britain to vote in the upcoming US presidential election took to the streets of London on Wednesday (Sept 21) in a red open-top double-decker bus adorned with anti-Donald Trump posters.

The organisers, online activist network Avaaz, put up flags, balloons and posters reading "American Abroad: Vote to Stop Trump" on the bus, referring to the Republican presidential nominee who faces Democrat Hillary Clinton in the Nov 8 vote.

Some 30 activists filled the top of the bus as it made its way around the British capital, chanting "Stop Trump" and singing along to Bruce Springsteen song Born In The USA.

The bus made stops along the way, with campaigners using tablets to help some expats register for the vote.

Some eight million Americans live abroad, of which more than 220,000 live in Britain. However, just 12 per cent of them vote, Avaaz said in a statement.

According to a Reuters/Ipsos poll published last week, Clinton leads Trump by 4 percentage points, with 42 per cent of likely voters supporting her and 38 per cent backing the Republican.