My understanding from reading the CAA's releases is that the problem in their eyes is that the Paris crash was caused by a single failure (the tyre).
It's normally understood that no single (and remotely probably) failure must be able to cause a fatal accident. CAA have I think withdrawn the type certificate until it is clearly shown that no single failure can cause such a disaster again.
For example the Kegworth crash was caused by a combination of an engine failure and a human-factors fault (shutting the wrong engine down). Still tragic, but a double failure case should be much less likely.
G