I find that a bit rich @NotALot when IIRC somebody said on SF to a poster that they were sick of their holier than thou attitude when the Brit poster said they spoke French when they were out and about. Although I have to say I might not remember the full gist of it as it was a long time back.
I have found the best way to learn French is to go to the market rather than a supermarket. It is only by practice and getting up the courage to speak that we improve. Nobody minds if you get it wrong or have a thick Brit accent. The French just seem to love that you are trying your best in my experience.
As for those who have been here 20 years or more and still do not speak, flout the laws… do not get me started. A French friend told me today that his dad was in hospital recently (nothing drastic at all thankfully). His dad speaks some English and was sharing a room with a Brit. The man had been here for 19 years but could not even speak enough French to ask for a glass of water! We are immigrants here. This is France and it is no longer Britain, so we need to show some respect to the locals.