The leader of the Scottish Liberal Democrats has stepped down from his post after a "disastrous" result for the party in the Scottish Parliament elections.
Tavish Scott said his party had been "up against it" since the coalition between the Liberal Democrats and the Conservatives took power in Westminster last year.
The Scottish Liberal Democrats suffered a heavy defeat in the Holyrood elections, losing deposits after 25 constituency candidates failed to gain 5% of the vote.
The Scottish Parliament will have just five Lib Dem MSPs, with no constituency seats on the mainland. They had 16 MSPs in the previous parliament.
Mr Scott told Sky News yesterday: "I have just no doubt that since last May we have been up against it because of the formation of a UK Government where the Liberal Democrats were seen to be propping up the Conservatives. And that's, I think, in Scotland, a pretty disastrous and toxic mix in politics.
"It's for the party now to decide how to move forward and I think that's best done with a new leader."
In a statement Mr Scott, who was elected leader of the party in August 2008, said he was resigning the leadership with immediate effect.
He said: "Thursday's Scottish general election result was disastrous and I must and do take responsibility for the verdict of the electorate.
"The party needs a new direction, new thinking and new leadership to win back the trust of the Scottish people.
"I am honoured to serve as Shetland's MSP in this Parliament."
Mr Scott held on to Shetland with a reduced vote share.
Former Lib Dem leader Charles Kennedy said Mr Scott was "handed mission impossible" in the Scottish elections, given the "current coalition unpopularity".
Paying tribute to him, Mr Kennedy said: "I am extremely sorry to learn of Tavish's decision to step down.
"He was handed mission impossible in the Scottish elections, given the current coalition unpopularity. That was always likely to be the case, as some of us warned at the time one year ago.
"Tavish is one of our country's most talented politicians and his response today is characteristically honourable. It deserves to be met by a response at a UK Liberal Democrat level which is similarly honest."
The Liberal Democrat leader, Deputy Prime Minster Nick Clegg, said: "I was very sad to hear of Tavish's decision.
"He has been an excellent and energetic leader of the Scottish Liberal Democrats at an extremely difficult time, as well as a good friend and colleague.
"I'm sure he would have done a brilliant job leading the fightback for the Lib Dems in Scotland but I fully respect his decision.
"I know that Tavish will continue to play a central role in supporting the new Lib Dem leader in Scotland and in Scottish politics as a whole."
Scottish Labour leader Iain Gray said: "Tavish Scott has served his party energetically and I am sure he will continue to serve his constituents diligently and effectively. I wish him well for the future."
SNP leader Alex Salmond said: "I have great respect for Tavish Scott, a distinguished parliamentarian with a significant contribution to continue making, and he carries my very best wishes for the future."
Earlier yesterday, the SNP's finance spokesman John Swinney said Mr Salmond, who has led the party to the first parliamentary majority in Holyrood history, told the Prime Minister that the party's resounding victory was a game changer.
Mr Swinney told BBC Radio Scotland's Good Morning Scotland programme: "The First Minister made clear yesterday his intention to discuss with the Prime Minister the importance of recognising the difference that Friday's result produces for Scotland.
"The difference is the people of Scotland have made it very clear that they want to see progress made on the questions of economic opportunity in Scotland, and on constitutional progress.
"The short-term opportunity to do that is by improving and strengthening the Scotland Bill, currently going through the UK Parliament, and that is the message that the First Minister gave to the Prime Minister."
The Scotland Bill is designed to give Scotland greater financial accountability but the SNP has argued it does not give the Scottish Government sufficient levers to grow Scotland's economy.
The Bill passed its final stage in Holyrood in the last term and is being debated at Westminster, but Mr Cameron has been told the outcome of the Scottish election should have a bearing on the outcome of these deliberations.
Mr Swinney, who led the SNP between 2000 and 2004, also rejected suggestions that Westminster could interfere with an independence referendum in Scotland.
He said: "We can legislate for there to be a referendum on independence within Scotland, and we will do that in the latter part of the parliament.
"But the early priority is to get the necessary economic and financial powers that will enable us to work our way out of the economic challenges that we face.
"We've done a lot in the last four years to deal with an exceptional period of economic turbulence."
He added: "The reason we need more economic powers is to better respond to that, and to deliver the type of opportunities the people of Scotland asked of us when they gave us such a handsome mandate in the election."
Scottish Conservative deputy leader Murdo Fraser called on Mr Salmond to "bring it on" and launch an immediate independence referendum, otherwise there would be a "very persuasive argument" for Westminster to steal his thunder.
He said: "Nothing would be more damaging for Scotland than to have four or five years of a long-running debate over whether we will be independent or not."
Scottish Labour deputy leader Johann Lamont recognised the challenge her party faces in choosing a new leader following the planned resignation of Iain Gray after the party was reduced to 37 MSPs.
She added: "It's a simple fact that if you lose as many seats that we've lost then you're choosing from a smaller pool of people."
Ms Lamont tentatively suggested that she could be up for the job.
She said: "I'm a potential leader because I'm deputy leader, but I've barely slept since Thursday so I'm not going make that decision now."
Annabel Goldie, leader of the Scottish Conservatives, said: "Tavish has played an important role in the Scottish Parliament as a former minister and as leader of his party. He has always conducted himself with courtesy and dignity. I wish him well for the future."