Boris Johnson has dodged questions over the tax status of Rishi Sunak's wife and said it was important to "keep people's families out of" politics.
The twice-divorced Prime Minister, who only confirmed how many children he had last year, refused to get into the row over Mr Sunak's wife Akshata Murthy who is registered as non-domicile in the UK.
"I think it is very important in politics if you possibly can to try and keep people's families out of it," he told reporters on a visit to Hinkley Point C nuclear power plant.
"What I will say is that Rishi and I are working very hard on a massive long-term British energy security strategy, that is what we are focused on.
"What we are focused on is making sure we have the investment going in now that will undo some of the strategic mistakes of previous decades."
His comments came despite four references to "family" in the ministerial code, for which he wrote the foreword.
But Labour leader Keir Starmer accused the Chancellor of "breathtaking hypocrisy".
He said: The Chancellor has imposed tax rise after tax rise on working people. And he's said time and again there's no alternative, we've got no option.
"If it now transpires that his wife has used schemes to reduce her own tax then that's breathtaking hypocrisy, and only goes to show it's more evidence of just how out of touch this Chancellor is.
"And I think he's got very, very serious questions to answer in relation to these schemes."
Ms Murthy, whose family business is estimated to be worth around £3.5bn, may have used the status to save money in tax over several years, including since 2019 when Mr Sunak started working at the Treasury.
The classification is not illegal and can save an individual from paying UK tax on income from dividends from foreign investments, rental payments on property overseas or bank interest. It also allows an individual to avoid inheritance tax in the UK.
A spokesperson for Ms Murthy said she did not claim non-dom status but she was automatically classified as such as she is an Indian citizen.
Business Secretary Kwasi Kwarteng claimed it was "completely unfair" to scrutinise her tax affairs, as she is a private citizen.
He told Sky News: "It's completely unfair to be bringing someone who is not a politician and essentially attacking them in a way that's happening.
"She made it very clear that as an Indian national she can't have dual citizenship and she's got non-dom status here in the UK.
"Now, after 15 years staying here she will be domiciled, but for the moment she pays tax on UK income, as I understand, and on foreign income she pays tax outside the UK - that's what non-domiciled status means."
He added: "I'm not here to comment on her tax affairs."
Mr Kwarteng also sought to defend Mr Sunak, who he said had always been transparent about his family's business affairs.
"People have always known that he comes from a very affluent family but the implication that there's been any wrongdoing is completely wrong," he told LBC.
It is understood the Chancellor registered his wife's non-dom status with the Cabinet Office when he was promoted as a minister in 2018.
It is not known exactly how much has been saved by Ms Murthy but The Independent cited sources who claim she has saved millions of pounds over several years.
Ms Murthy's spokesperson said: “Akshata Murthy is a citizen of India, the country of her birth and parent’s home. India does not allow its citizens to hold the citizenship of another country simultaneously.
"So, according to British law, Ms Murthy is treated as non-domiciled for UK tax purposes. She has always and will continue to pay UK taxes on all her UK income.”
It is understood the Treasury is aware of Ms Murthy's tax status and that under current law, she will automatically be deemed domiciled after living in the UK for 15 years.
Mr Sunak has not declared his wife's tax status on his MP register of interests.
The ministerial code states that ministers of state “must ensure that no conflict arises, or could reasonably be perceived to arise, between their public duties and their private interests, financial or otherwise”.
It adds that on appointment, ministers have to provide a list of all interests which “might be thought to give rise to a conflict”, this should also cover “interests of the minister’s spouse or partner and close family”.
Dividends from Infosys, the India-based company owned by Ms Murthy's family, calculated from her stake in the company, of 0.93 per cent - worth approximately £725 million based on recent market valuations - suggest the payments could have totalled around £11.6 million in the past year.
Representatives for Ms Murthy insist she has paid foreign taxes on foreign income.
