It means anything the utterer wants it to mean, therefore it doesn't mean anything to anyone. Usually used by idiots
An ex aquaintance of mine has a "fighting for Britain bulldog tattoo thingy on his arm. He's currently stationed at HMP Wandsworth, fighting for Britain. 5 years I believe. I think he's studied for loads of O Levels or whatever they call em now. 24 in total so far I reckon.
A case proven Patriotic Genius if ever there was one.