In a roundabout way. They can be a government in exile, somewhat as the 'official' French government was during WWII
During most of the second World War, Poland had a government in exile in London that was recognized diplomatically by most of the Allied Powers.
French General that fled to England and started a government-in-exile.
The head of the Polish Government in Exile during most of WW2 was Stanisław Mikołajczyk.
Charles de Gaulle was the leader of the French government in exile during World War II. He was also in charge of the Resistance Movement that battled the Germans during that time.
Charles de Gaulle was the leader of the Free French government in WWII. Like many of the other western European countries with "governments-in-exile", the members of the Free French government lived in England for the duration.
Charles de Gaulle .
Charles de Gaulle.
Charles de Gaulle
Charles de Gaulle
I can't find any evidence of a formal declaration of war on France by the British during World War 2. Put the Allies did fight the french. They fought the Vichy French Government (the pro nazi government that had surrendered in 1940 when it was blatantly clear the battle for France had been lost.) They also attacked the french fleet in the hopes of denying it's use to the German Navy. The Allies also took back the French colonies in Africa and the middle east until eventually, on 20 August 1944, the Vichy Government Officals fled France and created a government in exile and in early April 1945 surrendered and tried by Provisional Government of the French Republic: the government headed by Charles de Gaulle.
The French government split and the government in exile was on the Allied side while the Vichy government was on the axis side.