But the difference is OBVIOUS!
The Breton are French, and have been French for centuries. The British are guests, visitors. They are not French. It is always pleasant when an Anglophone can speak French, but nobody EXPECTS the British to speak French. They are British, after all. They're expected to speak English, and in areas that thrive on tourism, as Bretagne does, it is only to be expected that people will accomodate the tourists and visitors to the greatest extent feasible. The British speak English, and this is simply a fact. It is not a threat to the territorial integrity of France as a nation that English people, or Americans for that matter, come to France and continue to speak French. Why would anyone expect otherwise? And likewise, it is not a threat to the territorial integrity of France to accomodate these anglophones, whose visits and money are most welcome.
But with Breton, c'est une autre histoire. These people are French. They speak French. They are in the country of France. Most French people do not speak Breton. France is one country. If the Breton insist on regional particularism, such that the government itself should deal with them not in the French of France, but in an ancient provincial dialect, they will develop a national identity and nationalism that will draw them away from unity with France. If the Breton demand, and succeed, then the Flamands of Picardie will demand that the government deal with them in Flemish. And the Alsatians will demand to be dealt with in Alsatian. The Savoyards will insist on Italian, as will many of the people of Nice and the Cote d'Azur. The Corsicans will insist upon doing business in Corsican, the Provencals in provencale, Guineens in Indian languages, Tahitians in polynesian, and New Caledonians in the native tongue.
The country will balkanize and shatter into a dozen RACES, since "French" is not a race but a nationality held together by certain conventions. The Saxons and the Bavarians speak different dialects, but they are the same ethnic races. But the Bretons, Normands, Alsatiens, Provencales and Angevins are all of different ethnic races in origin. The concept of France and the abolition of the ancient provinces has weakened these ancient allegiances to the point that they provide color, but no FORCE.
But the Breton desire to have the state conduct business with them in Breton: this is a desire to give FORCE, political force, to a separatist concept, that being Breton is a separate and distinct identity from being French.
France as a nation is composed of many ancient tribes. It cannot retain its unity if these ancient tribes reassert their tribal identities. The Bretons, of course, may retain and celebrate their culture, and do, and half of Paris turns out for Les Printemps Celtes. But that is not the same thing as achieving special political rights. If the Breton get them, then everyone else will demand them, and France will become as Belgium, and the unity of 1000 years will be torn apart by petty provincialism and nationalism.
It makes sense to deal with the British in English. But it is dangerous to set the precedent of dealing with the French of Brittany in Breton. A Breton is French. Some of them may assert otherwise, but this is a romantic notion, and it certainly is not to be encouraged by going along with it.
The French are mostly of Italian, Greek and North African ancestry.
The closest "relatives" of the Breton are the Welsh and Cornish, although the Galicians in NW Spain should be counted in this group.
Who taught you the Breton were French? Was he French?