David Cameron has put pressure on George Osborne to make clear how much tax he pays as "potential Prime Ministers" were urged to make public their income.
The Prime Minister's official spokeswoman suggested the Chancellor would be expected to follow Cameron's lead after publishing his tax return at the weekend following the revelations in the Panama Papers.
In what appears to be a carefully stage-managed move, the comments pave the way for Osborne to make public his full income - and in turn heap pressure on Labour leader Jeremy Corbyn and shadow chancellor John McDonnell to do the same.
It also means Boris Johnson and other would-be Tory leaders are feeling the heat and pressure to follow suit.
Sources have indicated to HuffPost UK that Osborne could release details of his tax affairs this week, including his interest in his father's upmarket wallpaper business, Osborne and Little.
In the morning briefing with Lobby journalists, the PM's spokeswoman said: "(The PM) is willing to be transparent, that it's right for potential Prime Ministers to also do so.
"With regards to who is in charge of the nations finances, the Prime Minister takes the view Chancellors and Shadow Chancellors should show transparency too. But he is not recommending it should be the same thing for everybody else involved in politics."
Asked whether that meant senior Tories aspiring to be leader of the party, she said: "It means what it says."
A Treasury source told HuffPost UK: "We have been clear that the Chancellor has never had any offshore shareholdings or other interests.
"His income and interests are straightforward and declared publicly: his salary, rental income from a property in London and a shareholding in his father's firm, Osborne and Little.
"He is always happy to consider ways to offer even more transparency."
A spokesman for the Labour leader said that Corbyn sent the only version of his tax return to Her Majesty's Revenue and Customs, and his office was "working on it".
The Prime Minister published his tax return on Saturday night after eventually disclosing he sold off shares in his father's offshore investment fund before becoming PM.
Downing Street insists that Blairmore Holdings, whose activities were revealed in the ‘Panama Papers’ data leak last week, was not set up to avoid tax and says it is similar to offshore unit trusts invested in by pension funds used by millions of Britons.
No 10 released unprecedented details of the Prime Minister’s tax affairs this weekend, publishing a summary of his tax return, which revealed he had an income of more than £200,00 a year.
The return confirmed that he and his wife Samantha had made a £19,000 profit on investments in Blairmore Holdings.
The tax return also showed that he had received two £100,000 payments from his mother following his father’s death, payments which will not incur any inheritance tax on Mrs Cameron’s estate should she live beyond 2017.
Downing Street insists that such ‘tax planning’ is ‘normal’ for many families.
Blairmore Holdings was created in 1982 after Margaret Thatcher lifted currency exchange controls and allowed UK investors to set up in dollar-denominated countries like Panama.
Cameron will today make a “very robust” defence of his and his family’s tax arrangements in a Commons statement, and is likely to hit back at Labour MP Jess Phillips for launching a personal attack on his late father’s tax affairs.
Cameron will respond directly to Labour attacks, singling out Ms Phillips’ HuffPost blog in which she said that his father “didn’t pay his fair share of taxes”.