The leaders of Britain's main political parties are using the long weekend to make a final push to win over undecided voters before the general election.

Prime Minister David Cameron and his rivals are rallying supporters in the final weekend of campaigning before Thursday's vote.

Most opinion polls suggest that the ruling Conservatives and their main opponents, the Labour Party, are neck and neck, and the election results are widely expected to be inconclusive. Some form of coalition government appears likely.

In a speech to activists on Sunday, Cameron said he is the "only option" for prime minister to avoid a power-sharing deal between Labour and the separatist Scottish National Party — a "calamity for our country," he warned.