Initially, Mr Sunak’s spokeswoman insisted the Prime Minister’s tax affairs were “confidential”, as he prepared to publish his tax return in an attempt at transparency.
Mr Sunak’s finances are under renewed scrutiny after it emerged Mr Zahawi settled an estimated £4.7 million ($5.8 million) bill with HMRC while he was chancellor.
Mr Starmer tried to draw a link at Prime Minister’s Questions between Mr Sunak’s handling of the current situation and his billionaire wife Akshata Murty, who has held a non-domiciled status that could have reduced her UK tax bill.
“We all know why the prime minister was reluctant to ask his party chair questions about family finances and tax avoidance," the Labour leader said.
Rishi Sunak through the years - in pictures
Earlier in the day, Mr Sunak’s spokeswoman said he would publish his tax return “in due course” but would not say whether he had ever paid a penalty to HMRC.
“You wouldn’t expect me to get into the prime minister’s tax affairs, they are confidential,” she said.
“The tax affairs of an individual, irrespective of who they are, are confidential.”
Everything you need to know about Rishi Sunak - video
She would not commit to publishing six years of his tax returns, as David Cameron did while prime minister.
In the past, the spokeswoman repeatedly declined to say whether Mr Sunak had private health care as the National Health Service strains under a series of pressures.
She said it was not “in the public interest” to divulge the prime minister’s healthcare arrangements.
But this month Mr Sunak, under pressure, said he was registered with an NHS general practitioner but had used “independent” health care in the past.