By Ian Dunt Follow @IanDunt
Chris Huhne has stepped down as energy secretary after the Crown Prosecution Service (CPS) brought charges against him of perverting the course of justice.
It is the first time since records began that a Cabinet secretary has had to resign to face criminal charges.
His ex-wife, Vicky Pryce, also faces charges. The pair must appear in court on February 16th.
Mr Huhne branded the CPS decision "deeply regrettable".
He added: "I'm innocent of these charges and I intend to fight them in the courts and I'm confident a jury will agree. I am standing down and resigning as energy and climate change secretary.
"I will of course continue to serve my constituents in Eastleigh."
Mr Huhne has consistently protested his innocence. If found guilty, he faces a custodial sentence.
He is alleged to have asked Ms Pryce, his wife at the time, to take the penalty points for a speeding offence.
Director of public prosecutions Keir Starmer said: "The essence of the charges is that between March and May 2003, Mr Huhne, having allegedly committed a speeding offence, falsely informed the investigating authorities that Ms Pryce had been the driver of the vehicle in question, and she falsely accepted that she was the driver.
"Accordingly, summonses against both Mr Huhne and Ms Pryce have been obtained from Westminster magistrates court and those summonses will now be served on them."
Ed Davey, under-secretary at the Department for Business, Innovation and Skills, has been made energy secretary in a mini-reshuffle which did not involve any Conservative ministers.
He is a confident media performer, but the loss of Mr Huhne takes away a powerful Liberal Democrat voice at the Cabinet table.
Norman Lamb was moved into Mr Davey's old role. Jenny Willott became an assistant government whip. Jo Swinson was appointed private secretary to Nick Clegg.
There was no mention of David Laws, who had been widely tipped to return to government in an advisory capacity.
In his letter to Mr Huhne, Nick Clegg held out the prospect of him returning to government in the future.
"I fully understand your decision to stand down from government in order to clear your name but I hope you will be able to do so rapidly so that you can return to play a key role in government as soon as possible," he wrote.
Mr Huhne, who narrowly lost the leadership fight for the party against Mr Clegg, was a robust defender of Lib Dem policies in government, not least during the AV referendum, when he led the attack against Tory campaign tactics.