By-elections: Labour retains three seats
Labour has won three by-elections, retaining Commons seats in Croydon North, Middlesbrough and Rotherham.
It increased its share of the vote in all three seats, but its majority was down in Rotherham, where the previous MP had quit over expenses claims.
The UK Independence Party came second in Middlesbrough and Rotherham, and finished third in Croydon North.
In Rotherham, the Lib Dems fell from third place to eighth, behind the BNP, Respect and the English Democrats.
The party got less than 5% of the vote, losing its deposit, in two out of the three contests.
The Conservatives saw their vote drop in each of the seats, coming fifth in Rotherham and fourth in Middlesbrough.
UKIP leader Nigel Farage, who attended the count in Rotherham, called the result across all three seats "UKIP's most impressive result in Westminster elections so far".
"The political establishment is just going to have to wake up to the fact that UKIP is here and here to stay as a significant and rising mainstream part of British politics," he said.
Ed Miliband welcomed the results as an endorsement of "One Nation Labour", the slogan he is expected to fight the general election under, but said his party still had work to do to win back the trust of voters.
"Voters in Croydon, Rotherham and Middlesbrough have put their faith in a One Nation Labour Party standing up for young people trying to find work and standing up for people whose living standards are being squeezed," he said.
Business Secretary Vince Cable defended his party's results, saying the government was unpopular, but was dealing with a difficult economic situation.
"Both the coalition parties did very badly in the result yesterday and unfortunately that is part of the price you pay for being in government," he said.
Labour candidate Sarah Champion won in Rotherham with 9,866 votes to UKIP candidate Jane Collins' 4,648.
The BNP and Respect pushed the Conservatives into fifth place, while the Lib Dems lost their deposit, trailing in eighth - thought to be the worst by-election result in the party's history.
Ms Champion, chief executive of a children's hospice, said: "Cameron's Tories have shown what they think of Rotherham, and today this result tells David Cameron what Rotherham thinks of the Tories."
UKIP's campaign in Rotherham was boosted by a row over a local couple who had their foster children removed by the Labour council because they were UKIP members.
But worries about unemployment had proven to be more important to voters than the headlines about fostering, BBC political reporter James Vincent commented.
The Croydon North and Middlesbrough polls were triggered by the deaths of MPs Malcolm Wicks and Sir Stuart Bell.
In Middlesbrough, Labour's Andy McDonald, a solicitor for a trade union law firm and former councillor, won with 10,201 votes to UKIP candidate Richard Elvin's 1,990.
The Liberal Democrats came third, with the Conservatives in fourth place just three votes ahead of the Peace Party's Imdad Hussain.
In his victory speech, Mr McDonald told the people of Middlesbrough: "Tonight you have a new voice in Westminster, a voice that will speak up for working families who are having their budgets squeezed, young people who are struggling to find their first job and the millions ignored by this Tory-led government."
In Croydon North, Labour's Steve Reed - currently the leader of Lambeth Council - won 15,898 votes, beating the Conservatives' Andy Stranack by 11,761.
Again polling under 5%, the Liberal Democrats lost their second deposit of the night.
Mr Reed said: "Tonight the people of Croydon North sent a clear message to David Cameron.
"He cannot be the one-nation prime minister Britain needs if he stands by doing nothing while Croydon faces one of the highest levels of youth unemployment in London."
Mr Stranack, the best performing Conservative candidate of the night, said he was disappointed to come second in Croydon North, but ousting Labour had proven to be a "big challenge".
Respect had hoped to pull off a repeat of George Galloway's surprise victory in Bradford West in April, when he overturned a 5,000 Labour majority to romp home by 10,000, after winning over the British Asian Muslim vote.
But Lee Jasper, the party's candidate in Croydon North and a former adviser to Ken Livingstone, won just 707 votes, placing sixth, and Yvonne Ridley, the Respect candidate in Rotherham, came fourth with 1,778 votes.