Britain’s opposition Labour Party descended into chaos as it narrowly rejected a grass-roots attempt to force leader Jeremy Corbyn to campaign to remain in the European Union and reverse the outcome of the 2016 referendum vote.

The 119-year-old party’s annual congress turned into a showdown between its splintered pro- and anti-Brexit wings.

Opinion polls show Corbyn’s efforts to unite the two by either delaying a decision on departure or putting it in hands of voters in a likely early election have led to a dramatic drop in support.

But a motion to force the party to “campaign energetically for a public vote and to stay in the EU in that referendum” was lost in a show-of-hands vote that appeared too close to call, to many watching in the hall.

“In my view, it was carried,” congress chair Wendy Nicholls announced after surveying the hands of 1,200 delegates packed into hall in the south coast city of Brighton. “No, sorry, it was lost,” she corrected herself a moment later.

Nicholls dismissed pleas from one pro-EU delegate who jumped on stage to ask for a recount.

The results was a triumph for veteran socialist Corbyn and a blow for a clutch of leaders who broke ranks and tried to turn Labour into an unambiguously pro-European party. (AFP)