David Cameron and Jeremy Corbyn will go head-to-head for the first time since the Labour leader reshuffled his shadow cabinet. The prime minister had already mocked the left-winger during the mix-up of Labour's top team – when Cameron described the reshuffle as the "longest in history" – and the subject is likely to come up when the leaders clash across the House of Commons on 6 January.
National security has been a repeat theme of the Conservatives' attacks on Labour and the appointment of Emily Thornberry to the post of shadow defence secretary gives Cameron a further opportunity to raise the subject again. The Islington South and Finsbury MP was forced to resign ahead of the 2014 Rochester and Strood by-election as Ed Miliband's shadow attorney general amid accusations of snobbery.
Thornberry had shared a picture of a house in the seat, which had several St George flags and a white van outside the property. The 55-year-old is also a unilateralist like Corbyn and opposes the renewal of the UK's nuclear deterrent, Trident.
But Corbyn will able to renew his attack on Cameron over his decision to grant Conservative ministers a free vote on the forthcoming EU referendum, which will be held before the end of 2017. The Labour leader accused the prime minister of "botching" his renegotiation with Brussels and claimed his plan to stop EU migrants in the UK from accessing benefits for at least four years would be "ineffective".
"Last month I travelled to Brussels myself to meet European leaders, including prime ministers, to discuss the issues our prime minister has raised today. I learnt a lot in that meeting," Corbyn said on 5 January.
"I learnt that the prime minister has botched his negotiations with European leaders, I also learnt that many of our European colleagues have a very intuitive understanding of British politics.
"They know the prime minister has asked for help so that he can win a referendum he never wanted to hold. Does the prime minister now accept that his attempt to bludgeon leaders into accepting flawed reforms has failed?"
You can watch the bout on BBC Parliament, BBC2's Daily Politics, Parliament TV and Sky News from 12pm GMT. Also make sure to follow @IBTUKPolitics for live reaction and commentary on the debate.