Three former Cabinet members have called on pro-European ministers to get behind Tony Blair over the EU vote.
Some see Tony Blair as weakened over the issue
Writing in the Guardian, Peter Mandelson, Alan Milburn and Stephen Byers said defeat in the referendum would be disastrous for Labour.
Known as staunchly loyal to Mr Blair, the trio said he was the underdog in the vote on the European constitution.
They wrote that Eurosceptics had been "allowed to get away with the most outrageous misrepresentation".
The former ministers, who have never collaborated before in support of the prime minister, also warned against "hype" over some aspects of the treaty during negotiations.
"In negotiations, we should be tough but constructive, " they wrote.
"It would be a mistake to hype issues beyond their real importance in order to claim some famous British negotiating victory.
"Those tactics only heighten the perception that Europe is a conspiracy against the British national interest, when in fact it is a means of advancing our national interests through co-operation with our partners."
Former Health Secretary Alan Milburn told Sky News it was "fairly unusual" for three former ministers to have co-operated in this way.
But he said they felt it was important to correct misconceptions and "myths" about Europe.
And he added that his friend Mr Blair's appetite for the job of prime minister was "undiminished".
"I think he wants to carry on, assuming we can get through the next election."
Some commentators have expressed fears that the referendum will be used as an opportunity to vote on the popularity of EU membership or to punish Mr Blair.
The trio wrote: "The forces of anti-Europeanism have been allowed to get away with the most outrageous misrepresentation of the facts without being properly challenged and have been permitted to pile on the pressure for a treaty
referendum - substituting an arguments about process for one about content - without being adequately pushed back.
"If there is any lesson of last week, it is that there is nothing to be gained by giving ground to these people."