The director of pro-euro campaign group Britain in Europe is likely to step down after the organisation is restructured, the BBC has learned.
Blair had favoured an early vote
Simon Buckby is understood to be frustrated at the government's failure to pursue a coherent policy on the euro.
Pro-euro MPs reportedly believe the chances of a referendum being held before the next General Election have all but been extinguished by the Hutton inquiry.
Britain in Europe's campaign director Mr Buckby told BBC News 24 that he would consider his future in the post after his organisation had been restructured in the light of delays in holding a referendum.
"Britain in Europe certainly needs to restructure and prepare to fight a much longer campaign than we were expecting," he said.
"If a referendum is called we must be prepared to fight it and win it, " he continued.
But if the referendum was further delayed he said it was important Britain in Europe was financially secure with a long term strategy to take it into the next parliament.
"It may be right for other people to take over the leadership and my position at that time. But I will make my decisions about that once we have taken the necessary internal review."
No early euro poll
There is a growing feeling among pro-euro campaigners that any referendum should be delayed in the wake of Prime Minister Tony Blair's flagging popularity.
Mr Blair had left the prospect open of a referendum on joining the single currency next year, with campaigners believing his personal popularity could swing the vote their way.
However the Iraq war and the Hutton inquiry into the death of government scientist Dr David Kelly have seen Mr Blair's popularity ratings fall.
George Foulkes, Labour MP and member of Britain in Europe's advisory board, told the Guardian newspaper he did not believe there would be an early pro-euro campaign.
"It has been derailed by other things. I am reminded of Macmillan's phrase about 'events dear boy'. We have to accept the reality of that," he told the newspaper.
Another pro-euro MP on the Britain in Europe advisory board, Conservative Ian Taylor, told the Telegraph it was unrealistic to expect an early referendum.
"Earlier in the summer they were holding to the line that we could have a referendum in this parliament - then they ran into Hutton," he told said.
Chancellor Gordon Brown announced in June only one of the government's five tests for euro entry had so far been passed.
He will decide in his next Budget whether circumstances have changed enough to justify re-running the tests.
The government is due to publish a "paving" bill in the autumn to put the legislation in place for a referendum in the future.
Pro-euro campaigners see that promise as a "road map" for euro entry, while "no" campaigners dismiss the pledge as a token gesture.
The government also promised another series of euro road shows to counter anti-European attitudes.