The Tories have failed to make a much-needed election breakthrough in Scotland, as the Labour Party's vote held up north of the border.
Labour won 41 out of 59 seats, while the Tories ended up with just one MP, David Mundell.
Elsewhere, the SNP failed to reach its 20-seat target, while the Lib Dems also fell short in key target seats.
An exit poll predicted a hung parliament, with the Tories the largest party but without an overall majority.
It predicted the Conservatives would have 305 MPs, Labour would have 255 and the Lib Dems 61, while others, including the SNP, would have 29.
Argyll and Bute has yet to be declared, with a result expected later on Friday.
SCOTTISH SEATS TALLY
Labour - 41 (no change from 2005)
Lib Dems - 11 (no change from 2005)
Scottish National Party- 6 (no change from 2005)
Conservatives - 1 (no change from 2005)
TOTAL: 59 out of 59 declared
On the night Labour secured more than 40% of all votes cast, more than the last general election in 2005.
The party's campaign co-ordinator Douglas Alexander said it had secured "spectacular" results in Scotland.
The party regained two seats it had lost in by-elections; Dunfermline and West Fife from the Liberal Democrats, and Glasgow East from the SNP.
Apart from those results, the numbers stayed the same as the 2005 general election, with none of the parties able to break through in key targets seat areas.
Mr Mundell, who was the sole Scottish Tory MP in the last Parliament, held on to his seat of Dumfriesshire, Clydesdale and Tweeddale.
Brian Taylor, BBC Scotland political editor
Members of Team Brown are stressing that he would be entitled to attempt to form an administration even if he has lost his lead.
Constitutionally, that is absolutely correct. But, in terms of momentum, it presumably depends upon numbers - and upon perception.
Would the Liberal Democrats, for example, really be prepared to return to power a party which, across Britain, had palpably lost support?
He told BBC Scotland: "It wasn't my intention five years ago to be the only Conservative MP in Scotland and it certainly wasn't my intention tonight."
He said he was "delighted" to have increased his majority "on what has been a very good night for Labour in Scotland".
And while he said they had "fought a very good campaign" he added: "I'm not complacently brushing aside the fact that we haven't made progress in the number of seats of Scotland; we haven't and I accept that.
"That's something that we have to look at very seriously in the aftermath of this election."
But he insisted the Tories would still have a mandate in Scotland if his party formed the next government.
"This is a British general election where the total number of MPs at Westminster will determine the government - either in one party or a combination of parties - whatever emerges over the next few hours."
However, SNP leader Alex Salmond said it was "blatantly obvious" that people in Scotland had voted against the Conservative Party, and challenged their mandate to govern north of the border.
Mr Brown increased his majority by more than 5,000 votes
He said his party was "on course for our best result since the 1970s in a Westminster election".
The SNP secured 20% of the vote in Scotland but failed to win their top target seats, including Ochil and South Perthshire and Dundee West.
"This is a strong performance from the SNP with our vote increasing in key seats across the country," he said.
"The Lib Dems have failed in Scotland and are being pushed into third or even fourth place.
"The picture across the UK may be unclear, but it is clear the Tories have had a disastrous night as they have once again been decisively rejected across Scotland."
The Scottish Lib Dems also failed to make an impact on their target seats, including Edinburgh South and Aberdeen South.
But Tavish Scott, the party's leader, said: "We are on track to stay the second party of Scottish politics.
"We hold the same 11 seats we won in 2005 in the face of Labour's vote hardening up.
"We've made solid progress in some tough seats like Edinburgh North and Leith and Glasgow North and will build on that in the Holyrood elections next year."
Alistair Carmichael, the Lib Dem's Scottish spokesman, accused Labour of "scaring" people in Scotland.
He told BBC Radio Scotland's Good Morning Scotland programme there had been a "hardening" of the Labour vote in Scotland in the last few days.
He added: "Bluntly it has to be said that the Labour tactics of scaring people in Scotland, and the Tory party tactic elsewhere of doing much the same thing, seem to have worked."
But Scottish Labour leader Iain Gray denied his party had used scare tactics.
"Over the last three years, we've listened to the message of the electorate, we've articulated arguments which I believe resonate with them on issues like knife crime, clean hospitals, literacy in our schools," he said.
"And I think we got the benefit of that."
Mr Gray also claimed voters had used the election to pass judgement on the SNP administration at Holyrood.
"The electorate judged them quite harshly last night," he said.