Independent election monitors say under 46% of the electorate took part in Sunday's vote - the law requires at least 50% to make a ballot valid.

BBC: Montenegro vote ruled invalid

The Government is asking returning officers on duty at this Thursday's London referendum to count as valid as many ballot papers as possible, even those where the voter's 'X' does not quite hit the spot.

BBC: 'X' marks the spot

In some states, you need about 750, 000 valid signatures to get on the ballot, says Richard Winger, editor of Ballot Access News.

BBC: US election: The third-party candidates