Amidst reports Britain will as soon as Monday announce that it is freezing its plans to hold a referendum, European Commission President Jose Manuel Barroso renewed a call for the bloc's 25 members to refrain from unilateral action.
"I call on political leaders to show they are capable of being responsible, to show prudence," he said after meeting party chiefs in the EU parliament on Thursday.
"What I ask for now is that political leaders, in particular the heads of government, take no individual or unilateral decisions."
Foreign Office sources told Britain's Press Association news agency that a bill that ultimately would lead to a popular vote, initially expected early next year, will be delayed indefinitely.
The constitution was rejected in the
Netherlands by 61.6% of voters
In the wake of the Dutch poll, in which 61.6% of voters rejected the painstakingly assembled text, other officials have refused to speculate on the options, preferring to pause for a summit of EU leaders in two weeks.
The bloc was buoyed by news that Latvia's parliament had ratified the charter, aimed at improving decision-making in the bloc, but four other referendums are scheduled before the end of the year.
"For the time being we have not seen any member states saying we don't want to ratify," a hopeful commission spokeswoman Francoise Le Bail told reporters.
"It is important to take stock of what the situation is (until) the European Council meeting" on 16 and 17 June, she said, adding, "What will happen then is a big question mark. Nobody knows.
The constitution must be ratified by all members for it to take legal force, but officials fear that any early move by Britain would build on the domino effect set off by the votes in France and the Netherlands.
Abandoning it would effectively leave the expanding bloc without a road map, but moving forward with the best parts of it would be next to impossible, as so much horse-trading between states was needed to put it together.
"It is an extremely grave crisis for the treaty and for Europe in the wider sense"
Brussels' Free University
The "pause for reflection" before the EU summit will be a welcome break, according to Paul Magnette from Brussels' Free University.
"It is an extremely grave crisis for the treaty and for Europe in the wider sense," he said. "Tensions are so high that the priority now must be to find a climate of confidence in which the European Union can function."