@Freezingold the Chris Whitty and PHE have stated that the modelling they have done they believe will tell them pretty much exactly when to act.
The modelling data has not been released as far as I'm aware because people will react to it which then makes it less reliable.
The general public probably have a hundredth of the information available to the CMO and PHE. We are not going to be in a position to assess the decision making.