Britain’s opposition leader, Jeremy Corbyn, has confirmed that he will take a “neutral stance” in a second Brexit referendum if he becomes prime minister.

It follows mounting pressure to say which side he would take in the confirmatory poll that his Labour party proposes.

Labour, which on Thursday unveiled a manifesto brimming with public spending pledges, says it will negotiate a new Brexit deal with the European Union and put the outcome to a second national vote.

Corbyn said he would “be an honest broker and not campaign for either side in the final say referendum.”

The announcement came in a BBC debate hosted by Fiona Bruce in which leaders of the four main parties answered questions from a studio audience.

Boris Johnson was challenged about his government’s refusal to publish a report into Russian interference in British politics, but his answers were dismissed by the audience.

Earlier, the Brexit Party, led by anti-EU Nigel Farage, published a list of policy pledges in its manifesto.

The party is running in almost 300 seats but has withdrawn from 317 Conservative-held constituencies to avoid splitting the pro-Brexit vote.

Farage urged voters to give his party lawmakers in Parliament so they could pressure the government for a hard Brexit in which Britain wouldn’t remain aligned to EU rules and standards.

“Without us, there will be no genuine Brexit,” he said.