Tony Blair's announcement that Britain will hold a referendum on the proposed European Union constitution will be greeted with some trepidation by its supporters elsewhere in Europe, and by many other EU governments.
Europe's leaders may come under pressure to hold their own votes
The final text of the constitution has not yet been finally approved. But the chances are that it will be - after appropriate last minute haggling - at the next EU summit in June.
Beyond that, though, the future now looks more uncertain than ever.
Before Mr Blair's announcement, seven current and future EU countries had said they would or they might hold a referendum on the constitution: the Czech Republic, Denmark, Luxembourg, Ireland, the Netherlands, Portugal and Spain.
Now, there may well be pressure on others to follow suit - President Jacques Chirac in France, for example, and there is no guarantee of a "yes" vote there.
It is all likely to make it harder to get the final document approved.
There has already been criticism that Mr Blair is putting his own political fortunes at home above the wider European interest - trying to take the sting out of an issue which had the potential to loom large in a British general election expected in May 2005.
"The head of government of a major European country should not endanger such a central project as the EU constitution purely out of domestic political calculations," said the vice-president of the European Parliament, Ingo Friedrich of Germany.
"He obviously wants to avoid his own general election becoming a referendum on the EU constitution."
The Swedish Prime Minister Goran Persson, who does not plan to hold a referendum, said he would not be influenced by Mr Blair's decision in London.
"I think we are entering dangerous ground if we take that kind of decision-making away from parliament and put it to a referendum," he said.
Pressure all round
For some countries, though, a referendum is a legal requirement. It is not something which would follow a parliamentary vote, as Mr Blair is proposing, but the basic instrument of ratifying the constitutional treaty.
Two countries, Denmark and Ireland, have in the past held referendums on EU issues which have resulted in "no" votes, and the same could easily happen again there or elsewhere.
Unless the constitutional treaty is endorsed by all 25 members of the enlarged EU, it will not come into force, and any country failing to vote in favour will come under pressure from fellow member states to try and try again.
If eventually only one country holds out against the constitution, it could, as a last resort, be asked to leave the European Union.
But if the "no" vote was to come in a member state as large as Britain, that would be an extremely difficult thing to push through.
So Tony Blair has raised the stakes for everyone, and some of his fellow European leaders will not thank him for it.