This morning I asked Quentin (MSCC travel man) what the score was with this. Below is his reply.
"Hi Steve,
Legally required from 01 July – although local knowledge is that les Flics will not be enforcing the €17 fine for not having one until November.
The general opinion is that this is simply a cost saving exercise as they often have mass checks where a road is blocked off, and everyone has to blow in the bag – the cost in breathalysers to the authorities must be substantial, so they will now stop and ask you to use your own!
So you must have two, otherwise they can stop you, get you to use your last one and then promptly nick you for not having one!
Last month they were available on the ferry at £5.99 for two, or in Super-U at €1.50 for two (I must get my calculator to work out which is the best deal).
Cheers
Quentin "