Jeremy Corbyn will take on David Cameron at Prime Minister's Questions for the first time in a crucial early test of his Labour leadership.
After a turbulent start to his stewardship, the veteran left-winger will attempt to show his radical approach can trouble the premier.
Mr Corbyn has signalled he wants to make the weekly Commons showdowns "less theatrical" and more "factual". He has also suggested that his six questions could be shared out among senior colleagues in future.
The Tory ranks are under orders to restrain themselves from shouting down Labour's new chief, for fear such aggression could backfire by invoking public sympathy.
But Mr Corbyn's speech to the TUC conference on Tuesday showed he will not shy away from strong language.
The Islington North MP accused ministers of "declaring war" on workers with trade union restrictions and "knowingly" passing welfare changes that resulted in suicides.
Westminster will also be watching the Labour benches closely for signs of how they are adjusting to the new regime.
Despite Mr Corbyn's thumping victory in the leadership race, he was seen as having struggled to put together a unifying shadow cabinet after a slew of senior figures ruled themselves out.
Backbenchers and even frontbenchers signalled disquiet about his appointment of hardliner John McDonnell as shadow chancellor, and there have been complaints that no women were handed the most senior jobs.
Shadow justice secretary Lord Falconer has indicated he will resign if Mr Corbyn backs British exit from the EU in the looming referendum - a prospect the leader has refused to rule out.
Another potentially serious policy fault line emerged on Tuesday night when the freshly-installed shadow work and pensions secretary Owen Smith contradicted Mr Corbyn over whether the party wanted to abolish the Government's benefits cap.
Mr Corbyn told the TUC the cap amounted to "social cleansing".
He said: "As far as I am concerned, the amendments we are putting forward are to remove the whole idea of the benefit cap altogether."
But Mr Smith told Newsnight Labour was only opposing Government plans to reduce the benefits cap from £26,000 to £23,000.
He said it would be "foolhardy" for the party to "set our face unthinkingly" against a policy that had public support.
"I think the truth is we still must support overall reductions in welfare spending. I think we have also got to have limits on what individuals and individual families can draw down," he said.
"Can I be clear - our policy is to oppose the Welfare Bill which includes the reduction from £26,000 to £23,000 on the benefit cap for individual households."
Mr Smith was told several times that Mr Corbyn had said the cap should be scrapped altogether.
"No, our policy is to review that aspect of it," he said. "We are very clear. We are in favour of an overall reduction in the amount of money we spend on benefits in this country and we are in favour of limits on what individual families can draw down.
"Because I don't think the country would support us saying we were in favour of unfettered spending."
As he got to grips with the difficulties of managing a political party, Mr Corbyn was also enduring criticism of his conduct as a national political figure.
The republican was rebuked for refusing to join Mr Cameron and other guests singing God Save The Queen at a Battle of Britain commemoration at St Paul's Cathedral.
A spokesman for the Labour leader said he had listened to the national anthem in "respectful silence".