Chris Huhne faces pressure to decline a £17,000-plus severance payment available to him after he quit his job as a Cabinet minister to fight a criminal charge of perverting the course of justice.
As he faced a first day out of office, the wealthy Liberal Democrat politician gave no immediate indication on whether he would accept calls for him forego the taxpayer-funded financial help.
In a dramatic day at Westminster, Huhne announced he was resigning as Energy Secretary to mount a "robust defence" of claims he persuaded his then wife to take his penalty points for a speeding offence in 2003.
The MP for Eastleigh and his ex-wife Vicky Pryce, who faces the same charge, will appear before Westminster Magistrates Court on February 16. The charge carries a maximum sentence of life imprisonment.
The sudden departure forced a mini-reshuffle of Lib Dem ministers, with Ed Davey promoted to the Cabinet in Huhne's place and Mr Davey's business minister role taken by Deputy Prime Minister Nick Clegg's chief political adviser Norman Lamb.
Mr Clegg expressed hope that his former leadership rival, and one of the party's most prominent figures, would quickly prove his innocence and "return to play a key role in government as soon as possible".
Prime Minister David Cameron made no mention of a possible return in his own letter accepting Huhne's resignation though, saying only that he was sorry to see him leave "under these circumstances" and wishing him well for the future.
Huhne, 57, is the third Cabinet minister - and the second senior Lib Dem - to be forced out since the formation of the coalition in 2010, following David Laws and Liam Fox.
His departure will be rued by Lib Dems on the left of the party, who saw him as one of the ministers most able to stand up for their values against Conservatives in Cabinet.
And environmentalists voiced dismay at the loss of what Greenpeace described as "a vocal advocate for the green agenda in a Government whose green credentials are looking more than a little tarnished".
Announcing his resignation in a 30-second statement outside his London home, Huhne described the Crown Prosecution Service's decision to press charges as "deeply regrettable".
"I am innocent of these charges and I intend to fight this in the courts and I am confident that a jury will agree," he said - explaining that he was quitting to "avoid any distraction" to the work of government or his legal fight.
Pryce, a prominent economist, told the BBC she hoped for a "quick resolution" to the case.
The events which led to the charges date back almost a decade to March 2003, when Huhne's car was allegedly caught by a speed camera on the motorway between Stansted Airport in Essex and London.
Accusations of impropriety did not emerge until after the MP's 26-year marriage ended in 2010 as a result of his affair with PR adviser Carina Trimingham.
Pryce told the Sunday Times last year that her ex-husband - then an MEP - had asked "someone" to take the penalty on his behalf to avoid losing his driving licence.
Huhne and Pryce were interviewed by Essex Police detectives before the case was handed to the CPS, but a decision on possible prosecutions was delayed by a court battle to obtain key emails from the newspaper.
Director of Public Prosecutions Keir Starmer said the Crown Prosecution Service had concluded that there was "sufficient evidence to bring criminal charges against Mr Huhne and Ms Pryce for perverting the course of justice."
Labour led demands for Mr Huhne not to take the severance payment of three months' ministerial pay - a total of £17,207 - but he is also bound to face serious pressure from within his own party.
Opposition MP Chris Evans said the Lib Dem had shared a platform with Tory co-chairman Baroness Warsi in 2010 when she urged Gordon Brown's ministers to decline their rights under the 1991 Ministerial and Other Pensions and Salaries Act.
"If he didn't agree with her, he should have said so - so he should now forfeit the £17,207 he is entitled to.
"And if the Tories don't make it clear that they believe Chris Huhne should give up this payment, it will be clear that they think there's one rule for them and their Liberal Democrat friends and another for everyone else," Mr Evans said.
Asked whether Mr Huhne would be taking his payoff, Prime Minister David Cameron's spokesman said: "That's a matter for him." A Liberal Democrat spokesman said he was not aware of any decision having yet been made.
Other government changes among Lib Dems saw Jenny Willott appointed an assistant government whip and Jo Swinson take Mr Lamb's old post as parliamentary private secretary to Mr Clegg.