I've never seen a legal document stating exactly what is meant by supervision, therefore it is always open to interpretation. If an FI feels he is able to supervise from home, with a report of what happened during the day, then I would say that is legal. This is working on the principle that something is legal unless a document specifically states it is not.
Certainly, the CAA have issued some guidance in the past, but it was only ever advice and not legally binding that the FI must be present at the airfield. This is much like the arguments over letting a passenger have a go on the controls when you only have a PPL, or whether you should be on the ground when you send a student solo, you can argue all day but there is no guidance in the law, so it is all open to interpretation, and whatever the school/cfi is happy with.
Last edited by RTN11; 9th Mar 2013 at 12:30.