Are all the countries which base their law on the english system still members of the commonwealth?
See http://en.wikipedia.org/wiki/Legal_systems#Common_law
It looks like the Republic of Ireland and parts of the US legal system are non-commonwealth countries with English-based law. They were both in the British Empire at one point, though. Nowhere else in that list jumps out at me as being non-commonwealth, although I don't pretend to have memorised a complete membership list.