LONDON — Agreements on defense, security and the treatment of migrants were reached by President Emmanuel Macron of France and Prime Minister Theresa May of Britain on Thursday, as the two leaders sought to protect critical areas of cooperation while Britain prepares to withdraw from the European Union.

Anglo-French summit meetings are regular events, but with Britain’s scheduled departure from the bloc in March next year, this one has a particular resonance. The British withdrawal, known as Brexit, will bring to an end more than four decades of European integration, and 2018 will see tough negotiations on the future trading relationship between Britain and the remaining 27 nations of the bloc — talks in which France will wield considerable influence.

In a significant good-will gesture, Mr. Macron announced that the Bayeux Tapestry, which depicts the Norman Conquest of England, would be lent to Britain for display, allowing it to leave France for the first time in 950 years. That, Mr. Macron told a news conference, was part of an effort to deepen cultural ties and help the two nations make “a new tapestry together,” even as Brexit introduces new uncertainty into their relationship.

For her part, Mrs. May agreed to pay an additional $62 million to help reinforce security around the French port city of Calais, which has been a gathering point for migrants seeking to enter Britain. That money will be spent on fencing, CCTV cameras and infrared detection technology.