The initial question posted here is a good one.
There are 'grey' areas surrounding this. The 'answers' I feel are not that helpful or accurate (BOAC). If you want a straight answer then I believe that you can operate as a non-qualified crew if the actual conditions are CAT1 or better.
For an approach all you need is the relevant VIS. For a take-off JAR suggests that you need to be qualified with a VIS of less than 400m. This is slightly misleading as I believe a CAT1 crew can take-off in VIS of 150m. The airfield is required to implement safe guards when the VIS drops below 400m in order to allow movements. A low-vis qualified crew can take-off in 125m with state approval. After the initial training (ground/simulator) has been completed you can usually make an approach in VIS below CAT1 after one practice 'on-line' (depending on the sim used for initial training), otherwise after 3. For take-off you are immediately qualified.