Sajid Javid did not declare using offshore trust while he was working at the Treasury, it has been reported.
It comes after the former Chancellor was revealed to have enjoyed non-dom status before entering politics, and had an offshore trust - thought to have been located in a tax haven.
While the now-Health Secretary gave up his non-dom status in 2009, before entering politics, he retained the trust until 2012, by which time he was an aide to George Osborne.
While MPs are required to declare major shareholdings, they are not required to say where they are held.
Mr Javid declared shares in Deutsche Bank, his former employer, in the 2011 register of members' interests.
But approached about the trust by the Independent, a spokesperson declined to say whether the trust included these shares as well as other assets, including shares in other companies.
They also declined to say whether it was a ‘blind trust’, or where it was located.
There’s no suggestion of wrongdoing by Mr Javid, who says he has fully declared everything necessary to Parliament and tax officials.
When he shut the trust down in 2012, Mr Javid says he incurred a 50% tax rate, which he claimed had offset any “accrued benefit” from it.
“Sajid has been very open and transparent about his previous tax status in the UK and when he lived abroad. He has nothing further to add,” a spokesperson said.
But Labour ’s James Murray said it was “rank hypocrisy” for senior ministers to defend a tax hike this month, when they’d used beneficial tax arrangements themselves.
He said: “The public has a right to know which ministers have benefited from tax avoidance arrangements and how much money they have saved as a result,”