BERLIN — German Chancellor Angela Merkel is insisting that Britain can only keep full access to the European Union’s single market by continuing to allow free movement of people.

British Prime Minister Theresa May says she will invoke by the end of March Article 50 of the EU treaty, triggering formal negotiations about Britain’s exit. She also appears prepared to prioritize immigration controls over single market access.

Merkel emphasized Wednesday that Britain can’t have both things. She stressed that “full access to the single market is coupled, and inseparably linked, to acceptance of the four fundamental freedoms, and they include free movement of people.”

She said in a speech to German exporters that allowing an exception for one country would “lead to an extremely difficult situation” in the EU.