BRUSSELS — His 13th-floor office with its panoramic views was testament to the high status Claude Moraes had attained as a senior member of the European Parliament. But on a recent morning, it was empty, save his suitcase, a laptop and a phone on his bare desk.

That is because Mr. Moraes is British, and his time in Brussels is up.

For Britons back home, the formal departure from the European Union on Friday means very little in practice, as the country will obey European Union rules until the end of the year.

But it is different in Brussels. The longstanding British contingent in the European capital now has to disband, or regroup. Thousands of British permanent officials, lobbyists and others are actually staying in Brussels, and many have qualified for passports from Belgium — a nation that the British have more often mocked than admired.

But for Mr. Moraes and many others, it has meant joining the “Brexodus” of those quitting Brussels and their country’s 47-year engagement with its Continental neighbors, a cause to which many have devoted their careers.