LONDON -- Almost 40 years after Britain joined the forerunner of today's European Union, the debate over the country's future in the Union has quickened with a warning from a top E.U. official that any moves to renegotiate the terms of British membership could wreck the bloc.
Herman Van Rompuy, president of the European Council, the body that groups the 27 E.U. member states, said that the European Union had benefited tremendously from British membership and that Britain's departure would be like seeing "a friend walk off into the desert."
But Mr. Van Rompuy also suggested that the strategy developed by Prime Minister David Cameron to restore dwindling public support for keeping Britain inside the bloc was likely to fail.
In an interview published Friday in The Guardian, a British daily, Mr. Van Rompuy said that renegotiation could undermine the one part of the European Union that Mr. Cameron says he values most: the single market under which around 500 million Europeans can do business without barriers.
"If every member state were able to cherry-pick those parts of existing policies that they most like, and opt out of those that they least like, the Union in general, and the single market in particular, would soon unravel," he said.
The intervention from Mr. Van Rompuy highlights the fact that other nations are likely to resent a process under which Britain seeks to retain the parts of E.U. membership that it likes, while rejecting the rest. In order to renegotiate British membership terms, all other member states would have to agree on the changes.
And, if that sort of discussion begins, other countries may make demands too, including some that could weaken the single market which seeks to establish a level playing field on trading issues.
"All member states can, and do, have particular requests and needs that are always taken into consideration as part of our deliberations," Mr. Van Rompuy said in the interview. "I do not expect any member state to seek to undermine the fundamentals of our cooperative system in Europe."
Mr. Cameron argues that, to persuade euro-skeptical British voters to stay in the European Union, the country should loosen its political and social policy ties to the Union and refocus them around Europe's single economic market. He wants to renegotiate the terms of British membership and seek approval for the result of that negotiation from the public, possibly in a referendum.
Britain formally joined in the process of European integration in 1973, when it acceded to the European Economic Community. Two years later, after a change of government and negotiations on the terms of membership, it held a referendum in which around two-thirds of those who voted elected to stay.
One theory in Britain is that the euro debt crisis presents a new opportunity to re-fashion the process of European integration because the 17 countries that use the single currency may need to rewrite the Union's governing treaties in order to become more closely integrated. That could give Britain the chance to negotiate its looser relationship simultaneously as part of a grand bargain.
Mr. Van Rompuy suggested, however, that such a rewriting of the treaties might not happen because it might not be necessary.
"The treaties allow a considerable degree of flexibility and much can be done without needing to amend them," he told The Guardian. "It is perfectly possible to write all kinds of provisions into the treaties, but amending them is a lengthy and cumbersome procedure needing the unanimous agreement of every single member government and ratification."
Mr. Van Rompuy's comments come at a sensitive moment, ahead of a widely anticipated speech by Mr. Cameron, expected in mid-January, during which he might make the promise of a referendum explicit. Many of his own lawmakers now want Mr. Cameron to promise a straight "in or out" vote, though he has so far resisted.
The political mood within Mr. Cameron's Conservative Party has hardened against engagement with Europe, partly because of the rise in popular support for the U.K. Independence Party, which has campaigned for Britain to leave the European Union and for tighter immigration controls.
UKIP is expected to do well in the next elections to the European Parliament in 2014, which will be held under a proportional electoral system that favors smaller parties. The party is unlikely to win many, or even any, seats in British parliamentary elections, expected the following year, because these will be fought under a first-past-the post system that tends to favor mainstream parties.
The smaller party could, though, take enough votes from the Conservative Party to deprive it of the seats it will need to form the next government.world
This article originally appeared in The New York Times.