Polling closes on Wednesday in the contest to lead Britain's Labour, with Jeremy Corbyn tipped to defeat the challenge from Welsh MP Owen Smith amid deep divisions in the centre-left opposition party.

In an eight-hour meeting of party chiefs on Tuesday, Corbyn rejected a plan by his deputy Tom Watson to let the party's lawmakers vote on who should be in the "shadow cabinet" leadership in parliament.

Watson has also proposed giving the party's MPs and trade unions more power over the choice of future Labour leaders, in response to criticism of the current process by Corbyn opponents who say party members and supporters have too much influence.

Many shadow cabinet members resigned over the summer in protest at Corbyn's leadership and a majority of the party's MPs voted no confidence in him but the veteran socialist has clung on, saying that he has helped boost the party's membership to record numbers.

Some commentators have warned the party could split.

"Together we are very, very strong," Corbyn told supporters at his final campaign rally on Tuesday, also meeting volunteers making last-minute calls for party members to cast their postal ballots.

"Whatever the result is, we -- all of us -- have mounted the most incredible campaign, mobilised a lot of people, and we've actually changed the political discourse in this country," Corbyn said.

The polls officially close at 1100 GMT on Wednesday.

Smith, who has accused Corbyn of lacking leadership and failing to rally Labour supporters against Brexit, also issued a plea to his supporters.

"Our party is at a crossroads, and the choice we face is between renewing our party to pursue unity and power, or satisfying ourselves with ongoing division and opposition," said Smith, who was far behind Corbyn in a YouGov poll published last month.

The party's National Executive Committee held an eight-hour meeting on Tuesday where Watson put forward his plan for the shadow cabinet as part of efforts to heal deep rifts between Corbyn and his supporters and the MPs, who tend to be more moderate.

Corbyn has instead put forward a plan for party members to have a say on shadow cabinet elections.

Under the current rules, the party leader has the responsibility for appointing shadow cabinet members.

Source: AFP