Brighton: British Labour Leader Jeremy Corbyn would use Britain's United Nations Security Council veto power to block US President Donald Trump from launching a military strike on Iran.

The party's stance was revealed by Labour's justice spokesman Richard Burgon on the sidelines of the British Labour Party conference, under way in the seaside town of Brighton.

"Just imagine it, later this year at the United Nations Security Council, representing the United States of America, Donald Trump makes the case for the invasion and occupation of Iran," Burgon told Labour members at an anti-austerity fringe rally.

"He makes his case, sat opposite him, representing the UK is Prime Minister Jeremy Corbyn ... [who] responds very politely and simply says 'no, not on my watch'," Burgon said, receiving rapturous applause.