@ChessProblem Well perhaps "French" is correct and the particle is wrong? If you swapped out the indefinite particle for a definite one it would work. "the French" works here as a noun. "a French" does not work, nor will it ever, try as we might.
@angiesliverpool I lived just round the corner from there on Picton road. The Post Office in the photo was run by a lovely couple, we always had a good laugh. Miss that place. And the ASDA! :)