PARIS (Reuters) - Britain would only be granted an extension to the Article 50 Brexit negotiation period if its parliament passed the deal on the table or if a clear alternative plan emerged by next week’s EU summit, a French official said on Friday.

The British parliament voted overwhelmingly on Thursday to seek a delay to the March 29 exit date enshrined in law, but how Britain’s divorce from the European Union will pan out is still uncertain. Options include a long delay, exiting with British Prime Minister Theresa May’s deal, which would require a short technical delay, leaving without a deal or another referendum.

“Without clarity - an adoption of the Withdrawal Agreement or a clear alternative - a no-deal would prevail,” the official at President Emmanuel Macron’s office said.

A short extension of a few weeks if May’s deal was passed next week would be granted by the other 27 EU members at a summit in Brussels next week, the official said, but not if May’s deal failed for a third time.

A long delay would only be acceptable if May put forward a clear alternative or proposed a second referendum or an election. “This request would be considered, but it’s not a given,” the official said.

“If the UK kept a seat at the table, with all its rights and duties, this could endanger the functioning of European institutions and the European project,” the official said.

That means EU leaders would request that the UK commit to not obstructing EU decision-making if it remained a member for a longer period, which would include EU budget negotiations.

“There could be a legal or political agreement meant to keep the UK out of some European decisions,” the official said. “These two fundamental points will be part of our criteria to consider the (extension) request.”