The move by Associated Newspapers, publisher of the Daily Mail, the Mail on Sunday and the Evening Standard, follows a private meeting within the past two weeks between Tony Blair, the Labour leader, Lord Rothermere, chairman of Associated, and Sir David English, editor-in-chief of its titles.
The Standard, London's influential evening paper with a readership of hundreds of thousands of commuters, is expected to back Labour, with the other two titles playing the role of honest brokers. That will mark a dramatic departure for the Daily Mail, which in recent elections has been a thorn in Labour's side.
Speaking from Paris yesterday, Lord Rothermere said: "The Daily Mail is independent. It has always embraced the policy of the Tories because the policy of the Labour Party was not acceptable.
"This is the most original situation where we have two political parties with policies not terribly different, the difference being the question of credibility."
He added: "I don't think we will actually endorse anybody. I don't believe in newspapers endorsing or supporting parties... The main and proper duty is to report what happens."
But he hinted that did not apply to the Standard, edited by Max Hastings, which is expected to endorse Labour. Asked whether this is likely, Lord Rothermere replied: "I wouldn't be surprised at anything Max Hastings does."
That newspaper on Fridaycame close to calling on voters to eject the Tories, arguing in a leader on sleaze that "the prospect appeals of at least a change in the cast of scoundrels".
Lord Rothermere said he "kept in touch" with both parties' leaders but has seen Tony Blair and Gordon Brown, the shadow Chancellor, "recently". The most recent meeting took place at a dinner at Associated Newspapers' Kensington headquarters at which Sir David was also present.
Only the opposition of the Daily Mail's editor, Paul Dacre, is thought to have stopped the paper giving its full backing to Labour. He is said to be arguing it would be a commercial mistake, angering die-hard Tory readers.
Last week Labour won over the Sun,which in 1992 ran a vitriolic campaign against Neil Kinnock. The Opposition still hopes to win the endorsement of the largest-selling tabloid, the News of the World, for whom Mr Blair has written an article today.
Election 1997, pages 21-24