Liz Truss and Rishi Sunak will go head-to-head in a TV debate after the battle to become the next prime minister became toxic with the two rival camps clashing over immigration, China and the economy.

The BBC debate at 9pm comes after a weekend that saw allies of the two Tory leadership hopefuls trade increasingly personal attacks.

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The Northern Echo:

Both candidates will spend Monday engaging in final preparations ahead of the first showdown between the two.

Sophie Raworth will host the debate in Stoke, with the BBC’s political editor Chris Mason and economics editor Faisal Islam offering analysis and some follow-up questions.

The studio audience will be made up entirely of people who voted Conservative at the last general election.

With postal ballots set to arrive on Tory members’ doorsteps by August 5, Mr Sunak faces pressure to use the BBC debate – and another hosted by TalkTV and the Sun on Tuesday – to make an early breakthrough.

Although he comfortably won the leadership race among Tory MPs, bookmakers have made Ms Truss favourite after a series of opinion polls and surveys put her firmly ahead with Conservative members.

Mr Sunak will meet Tory members at low-key events on Monday and will use the debate to” make a positive case for Britain’s future, debating all kinds of policy areas, including those he has already set out detailed plans for over the last few days, including immigration, Covid backlogs and foreign policy”, a campaign insider said.

The former chancellor’s major foreign policy announcement was a tougher line on China, which he called the “biggest-long term threat to Britain” – but allies of Ms Truss hit back, claiming he had argued for closer economic ties while in the Treasury.

In a hardening of tone against Beijing, Mr Sunak promised to close all 30 of the country’s Confucius Institutes in the UK.

Funded by the Chinese Government, they are ostensibly culture and language centres but critics have labelled them propaganda tools amid worsening relations between the West and China.

Mr Sunak accused China of “stealing our technology and infiltrating our universities”, pledging to work with US President Joe Biden to stand up to China at home and abroad.

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But those claims were met with scepticism by Truss supporters, with former Tory leader Sir Iain Duncan Smith saying “over the last two years, the Treasury has pushed hard for an economic deal with China” despite sanctions against him and other MPs and peers and a record of human rights abuses.

In a message to Mr Sunak he said: “After such a litany, I have one simple question, where have you been over the last two years?”Mr Sunak also came under pressure from his rival over his strategy to combat illegal migration, as he seeks to win over the Tory grassroots voters who will decide the next Conservative leader.

Calling the current system “broken”, he offered a 10-point plan on Sunday that included a commitment to a narrower definition of who qualifies for asylum compared to that from the ECHR, with enhanced powers to detain, tag and monitor illegal migrants.

Mr Sunak also promised to give Parliament control over who comes to the UK by creating an annual cap on the number of refugees accepted each year, albeit one that can be changed in the case of sudden emergencies.

But those proposals were picked apart by Truss allies, who raised questions about Mr Sunak’s proposals, arguing that it was unclear how the refugee quota would work and suggesting that some of his plans amounted to a “rebrand”.

Allies of Ms Truss also queried a suggestion from Mr Sunak that illegal migrants could be housed on cruise ships, something the Truss camp suggested would amount to arbitrary detention and a breach of both domestic and international law.

The Truss campaign had said that as prime minister she would increase the UK’s frontline Border Force by 20% and double the Border Force Maritime staffing levels, with Ms Truss claiming that her plan to tackle illegal migration would be given a strong legal foundation by the new UK Bill of Rights.

The plans from both candidates generated anger in some quarters, with Oxfam labelling as “cruel” any plan to link UK aid payments to countries’ co-operation with immigration removals and Amnesty International saying that making policy only to please Tory members has caused “chaos and backlogs”.

Ms Truss unveiled plans to boost UK growth rates with “full-fat freeports”, a move that may be seen as a bid to steal a march on Mr Sunak, who has been an advocate of free ports since his days as a backbench MP.

Pitched as the cornerstone of her tax-cutting economic vision, the Truss campaign said that the plans would see brownfield sites and other locations turned into “investment zones”.