British Conservatives Rishi Sunak and Liz Truss Thursday began their first grilling in front of party members as they wage a bitter duel to succeed Prime Minister Boris Johnson.

The hustings in Leeds, northern England, was the opening bout of 12 nationwide grassroots events as the members elect a new leader, after a cabinet revolt forced scandal-hit Johnson to quit.

The result will be announced on September 5, and Truss has built up a strong lead in surveys of Tory members after vowing immediate tax cuts as Britain confronts a slump in living standards.

Liz Truss held a campaign event in Leeds ahead of her hustings clash with Rishi Sunak in front of party members
Liz Truss held a campaign event in Leeds ahead of her hustings clash with Rishi Sunak in front of party members POOL via AFP / HENRY NICHOLLS

Former finance minister Sunak has denounced Truss's "fairy tale economics", vowing to tame surging inflation first, but has admitted that he is the "underdog" against the foreign secretary.

On foreign policy, both rivals have vowed to extend Johnson's staunch support for Ukraine, and to resist China's increasingly authoritarian rise, while profiting from vaguely defined "Brexit opportunities".

Their two televised head-to-head debates so far were fractious -- although the second on Tuesday was abruptly halted when the TalkTV moderator fainted live on air.

In Leeds, the candidates were allocated seats close together for the two-hour hustings, rather than squaring off at lecterns from opposite ends of a TV studio.

Rishi Sunak admits he is the 'underdog' against Liz Truss
Rishi Sunak admits he is the 'underdog' against Liz Truss POOL via AFP / Joe Giddens

The Tory members in attendance applauded co-chairman Andrew Stephenson when he observed that their party is poised to appoint Britain's third woman prime minister, or its first one of colour.

Sunak joked that he had got a "great tan" after criss-crossing the Leeds region in rare sunny weather this week.

After two head-to-head debates on TV, Liz Truss and Rishi Sunak clashed in front of Conservative members for the first time in Leeds
After two head-to-head debates on TV, Liz Truss and Rishi Sunak clashed in front of Conservative members for the first time in Leeds POOL via AFP / Jacob King

Truss went to high school in an affluent suburb of Leeds, while Sunak's Westminster seat lies about an hour's drive north in the same county of Yorkshire.

Truss said her Yorkshire upbringing had given her "grit, determination and straight-talking".

"And that, my friends, is what I think we need now in Downing Street," she told the hustings audience.

Truss, however, has also accused her Leeds school of fostering "low expectations" among its students, prompting anger from teachers and contemporaries.

Despite the school's apparent failings, she went on to the University of Oxford, like Sunak.

Both the candidates have vowed support for Johnson's "levelling up" agenda of revitalising growth in neglected regions of the UK including around Leeds.

Ahead of the hustings, Truss backed a railways investment project to help "turbocharge investment" in northern England, after Johnson and Sunak's Treasury scaled it back on grounds of cost.

"The thing about me is I'm prepared to take on the Whitehall orthodoxy, I'm prepared to challenge the groupthink that has, over decades, not put enough investment into this part of the country," she said.

But Truss declined to commit to restoring a separate high-speed link to Leeds, which has been scrapped under a mammoth project currently under construction to build new express lines out of London.

Addressing Britain's cost-of-living crisis, Sunak has reversed course on his previous opposition to increasing tax relief on household energy bills, which are set to rocket anew in October.

"I will grip inflation and get it back down," he said at the hustings, vowing tax cuts in future.