Labour could have lost the last election - and could lose the next one if it moves to the left, a Birmingham MP and Government Minister has warned.
Health Minister Liam Byrne, MP for Hodge Hill, also warned Labour's party machinery is "not up to the job" in parts of the country, in a hard-hitting study published today.
In an analysis of the last election, produced for leftwing think-tank the Fabian Society, he said the Conservatives, not Liberal Democrats, were best placed to take seats from Labour at the next election.
His conclusions come amid speculation Labour could move to the left when Tony Blair resigns as leader.
Gordon Brown, tipped to replace him, is believed to be opposed to some of Blair's health and education reforms.
The paper drew on the Labour Party's own internal seat-by-seat analysis of the 2005 result, which is expected to be a hot topic at Labour's first post-election party conference, next week in Brighton.
In his paper, Why Labour Won, Mr Byrne warned party colleagues that Labour risked defeat in the next General Election if it responds to Lib Dem gains in May by moving to the left. The Lib Dems are seen as more left wing than Labour on many issues.
He said: "A sharp swing to the left won't take us back to the glory days of 1997 - nor will throwing in the bin the reform manifesto on which we've just stood and won.
"But it's equally true that we didn't poll our full support.
"Radical party reform is vital if we want to mobilise every single Labour sympathiser in 2009."
He warned that the Labour Party needs to keep together the coalition of voters, including people from across the country and of all social backgrounds, that allowed it to win in 1997.
He said: "The truth is that Labour could have lost the election.
"The 2005 election was the closest election for 30 years and the final margin of victory - at just 770,000 votes - was just 1.8 per cent of registered voters. We could have lost our overall majority and our right to govern Britain."
But he said many Liberal Democrat voters had actually opposed Labour because they were concerned about "right wing" issues such as asylum, crime and anti- social behaviour.
Furthermore, many seats which Labour lost to the Lib Dems, such as Yardley in Birmingham, were traditionally Tory seats.
The Lib Dems took votes from Tory voters to win here, he said.
And he warned that the Conservatives, not the Lib Dems, were the challengers in 88 of Labour's 100 most marginal seats.
Mr Byrne said voters had higher expectations than ever before of public services, and would judge Labour by how successful the party was in reforming them.