Labour's by-election victory was a "verdict on the Government's failed economic plan", Ed Miliband said today.
The party held Feltham and Heston with an increased majority over the Conservatives.
Addressing supporters in Feltham town centre, Mr Miliband called on the Tories to "listen" to voters.
He said: "I think it is pretty offensive that the Conservatives are saying this morning 'well, what do you expect? It's a traditional Labour area'.
"They shouldn't be denying the people's choice, they should be listening to the people's verdict.
"I think that is one of the things people really don't like about this government - that they don't listen. They really need to start listening."
Labour's candidate Seema Malhotra was returned with majority of 6,203 - a net swing of 8.6% from the Conservatives.
On a night which saw a turnout of less than 29% - the lowest in a by-election for 11 years - the Liberal Democrats managed to see off a challenge from the UK Independence Party to hold on to third place.
Mr Miliband said Labour still had more to do to "rebuild trust" in politics.
He has come under increasing pressure over his leadership after a string of poor poll ratings.
Pressed on whether there was a question over his performance, he replied: "The most important thing about this result is what people here are saying in our country.
"Because this is a result about young people looking for a job, it's about families and their living standards and it's about businesses that are really struggling. What we are going to do as a party is focus on those people and fight for those people."
Ms Malhotra said the message on the doorstep was that the Government has failed the people of Britain.
She added: "This is a time when Britain needs to know that there is a Government investing in Britain, not a Government that is turning its back on what British families and businesses need."
The Conservatives said Labour should have extended their majority even further if they were looking to be on course for victory at the next general election, set for 2015.
The defeated Tory candidate Mark Bowen insisted that he was "proud" of the result, despite seeing his party's share of the vote fall.
"We have done a lot better than the pollsters and bookmakers suggested we would do," he said.
For the Lib Dems there was relief that they avoided the humiliation of being beaten into fourth place, despite a sharp fall in their share of the vote.
Lib Dem candidate Roger Crouch said: "We have shown that we are still resilient and still relevant."
However Ukip leader Nigel Farage said the Lib Dems were "almost a busted flush".
"People are turning to Ukip as they realise we are serious when it comes to putting Britain first," he said.
Ukip had been hoping to overhaul the Lib Dems but admitted their chances had been damaged by David Cameron's decision to wield the veto at the Brussels summit, which gave the Tories a fillip in the final week of the campaign.
Labour increased their share of the vote from 43% at the general election to 54% with a net swing of 8.6% from the Tories.
The Conservative vote share was down from 34% to 28%, while the Lib Dems dropped from nearly 14% to under 6%.
In contrast, Ukip saw its vote share more than double from 2% to over 5%.
The parliamentary by-election was sparked by the death last month of veteran Labour MP Alan Keen after he lost his battle with cancer.