Simon,
good luck practicing ANY french language in Paris.
As an American; they just ignored me; attempting with my "classroom french" to communicate. They all spoke fluent english ( perhaps better than some Americans do) however they would not acknowledge us. The rudeness was obvious.
Americans laugh at the way the French; especially Parisians, are so rude to mostly American tourists. Some say it has to do with how we mutilate the French language...so if you are going to say it in French; you had better pronounce it perfectly. Although as a UK citizen they may be more accepting of you; or maybe not.
The Canadian French are far more supportive if you are tryiing to speak to them.
The European community in general is charitable to english speaking Americans, thank goodness.