Rishi Sunak was asked to say whether David Cameron would “give full public disclosure of his work for Chinese interests”.
Labor leader Sir Keir Starmer pressed the Prime Minister over Lord Cameron's project for a Chinese investment fund, which he claimed may have links to the Chinese state.
Former prime minister Lord Cameron was appointed foreign secretary in Mr Sunak's reshuffle on Monday.
The reshuffle also saw the ouster of former Home Secretary Suella Braverman, with Mr Sunak hailing a new “strong and united team” in government.
On Tuesday, he accused Mr Sunak in a broad walkout of being “uncertain” and “weak”.
Speaking at Prime Minister's Questions, Sir Keir said: “The Prime Minister obviously thinks so little of his MPs that he has had to remove David Cameron from his seven-year exile in a shepherd's hut and make him Foreign Secretary.
“But a few months ago the Intelligence and Security Committee said that the now-Secretary of State's role in a Chinese investment fund may have been, and these are their words, engineered by the Chinese state.”
He added: “When will he instruct the Secretary of State to give full public disclosure of his work for Chinese interests?”
Prime Minister Rishi Sunak said he was “delighted” to have Lord Cameron back, saying his “unrivaled experience” would help Britain navigate an “uncertain world”, adding: “Like every other government minister, he will go through the normal process with the independent consultant.”
He said China presented an “era-defining challenge” and accused the Labor Party of “taking almost £700,000 from an alleged Chinese agent”.
Meanwhile, Labor leader Sir Keir claimed Ms Braverman was “unfit for office” as home secretary and asked the prime minister if he felt “ashamed” of putting her in office.
Mr Sunack said the Conservatives had “restored the economic security of this country” after a period of Labor government, adding: “It's a bit rich to be lectured on security by a man who wanted to make (Jeremy Corbyn) prime minister our country”.
But the Labor leader hit back at the Prime Minister's record, telling the Commons: “He's had three reshuffles, a forgotten conference speech, an empty King's speech, he even found time to fan Elon Musk, but none of them did the slightly different from the life of the workers.
“If we had a pound for every time we reset, the cost of living crisis would have been over a long time ago.
“He likes to think of himself as the man from Silicon Valley. The tech-savvy Californian. The country's first AI Prime Minister.
“And yet his big idea is to keep turning his government on and off at the wall and hope we see signs of life.”
Echoing Lord Cameron's words at Prime Minister's Questions, Sir Keir asked Mr Sunak: “Is he starting to feel that, as someone once said, he was once the future?”
The Prime Minister claimed he had “slightly missed the bottom” of Sir Keir's question due to shouting from MPs and while he welcomed the Labor leader's question on the cost of living, Mr Sunak mixed his words on high prices, claiming that was “the number one challenge facing countries above and below the family.”
The Prime Minister continued: “He mentioned it, but what he failed to acknowledge and talked about implementing policies, today was the day we kept the most important promise I made to halve inflation.”