The principal architect of the European Union constitution says Britain will be left on the sidelines of Europe, if it rejects the treaty in a referendum.
The warning about Britain's place in Europe comes from Valery Giscard d'Estaing, the former French president, who chaired the committee that drafted the constitution.
Mr. Giscard d'Estaing told British radio on Thursday that if some countries, like Britain, decide not to adopt the constitution, they will be left behind, if the majority of European countries move ahead with greater integration.
"If, by bad luck, the British finally said 'no,' and the other Europeans said 'we want to go,' then they will have to find an accommodation," he said. "And, it is true that, in that case, Britain will not be in the core of the system, but on the margin of the system."
Mr. Giscard d'Estaing was reacting to British Prime Minister Tony Blair's surprise announcement last week that the constitution being negotiated in Brussels will be voted on in Britain in a referendum.
No date has been set, but political commentators believe Mr. Blair will wait until after a general election, expected about a year from now.
The Blair government admits it will have a hard time winning over a skeptical public, as polls indicate most Britons believe the constitution would rob their country of sovereignty over many aspects of public policy.
The opposition Conservative Party on Thursday opened its campaign for European parliament elections in June with an assault on the proposed constitution by its leader, Michael Howard.
"Conservatives don't want a European constitution," he said. "Countries have constitutions, and we don't want to be part of a country called Europe."
Britain's announcement of a referendum has increased pressure for a similar vote in other EU countries. Luxembourg says it also plans a referendum, but French President Jacques Chirac told a news conference Thursday it is too early to decide the matter.