Phil Heatley's political future now hangs on an Audit Office investigation finding him to have been foolish with his ministerial expenses rather than trying to rip off the taxpayer.
However, his chances of returning to the Cabinet following yesterday's resignation from his housing and fishing portfolios look slim, given expectations among National Party colleagues that more cases of erroneous expense claims will be turned up by the inquiry.
Party sources indicated that Mr Heatley had pushed hard up against the limits of what was allowable when it came to claiming taxpayer-funded housing, travel and other allowances.
The Prime Minister has not ruled out his returning to the Cabinet, but that will require Mr Heatley getting a clean bill of financial health from the Auditor-General, Lynn Provost.
If that does not happen, a new Cabinet minister will be appointed, possibly Nathan Guy, who is a minister outside the Cabinet, or one of two Hawkes Bay MPs - Chris Tremain, the chief whip, or Craig Foss, chairman of the finance and expenditure committee.
Mr Heatley requested the Audit Office examination of all his expenses after John Key discovered a further lapse in his minister's use of his ministerial credit card.
The Whangarei MP had bought two bottles of wine costing $70 for his table at the National Party conference in Christchurch last August. He did not provide a full invoice and later signed off on a reconciliation form that described it as "dinner".
The Prime Minister's staff noticed it when inspecting Mr Heatley's paperwork after earlier revelations this week that the minister had misused his credit card, including for personal spending, which he later reimbursed. The repayments included the $70 for the wine.
He claimed at the time that he was unaware of the rules surrounding the use of the Ministerial Services credit card and had apologised and cut it up.
Mr Heatley tried to resign on Wednesday night after Mr Key's office told him about the document and asked the Auditor-General to review his expenses. Mr Key told Mr Heatley to sleep on it.
But the minister insisted on handing in his ministerial warrant yesterday morning.
Mr Key said he had not intended to ask Mr Heatley to resign and it was possible he was being too harsh on himself.
Ms Provost's staff began investigating Mr Heatley's expenses yesterday and Mr Key hoped she would be able to report back within two to three weeks.
The Prime Minister said there was no question Mr Heatley had misused his credit card but he did not believe it had been done dishonestly. The minister had been "stupid and silly".
The PM said the Auditor-General needed to consider the document Mr Heatley had signed and whether it was sufficient for wine to be described under the definition of "dinner".
He said Mr Heatley had rejected his suggestion to stand down temporarily "because he feels very passionately that he's honest and upfront and he has offered his resignation because he's taking it seriously".
Yesterday, Mr Heatley said he was "embarrassed and immensely sorry".
He said while his initial blunders were careless - the result of his ignorance of the rules - the discovery he had signed off the $70 as "dinner' had pushed the matter over the edge.
He wished to remain in Parliament as member for Whangarei but did not want to be a distraction from the Government's policy programme.
"I think I need to spend a long time on the backbenches."
Yesterday's resignation also brought fresh questioning of other Cabinet members, including Economic Development Minister Gerry Brownlee, who had to repay $152 for a lunch for the staff of his Ilam electorate office in Christchurch.
Mr Brownlee said he had no intention of following Mr Heatley's lead.
Mr Key said he had also checked Mr Brownlee's original documents and was satisfied they were accurate, stating only "lunch with staff".
The Prime Minister has also asked the Auditor-General to help Ministerial Services review its own procedures after it failed to define for ministers what was acceptable practice in the use of their credit cards.
* Age: 42
* Born and educated in Whangarei.
* He has been Whangarei MP since 1999.
* Resigned ministerial position over the purchase of two bottles of wine, and others including a Burger King meal, on his Ministerial Services credit card.
* Gives up his ministerial salary of about $243,000 for an MP's salary of $131,000.
* Housing allowance drops from about $37,000 to $24,000 a year.