DECs are a great idea. Unlike EPC they provide clear information to the occupants of a building about how their energy use compares with that of others.
What's more, the regulations require that the DEC be renewed annually and the new certificate will clearly show whether energy use is improving or getting worse. Since the certificate must be displayed in a public area, the expectation is that this will encourage occupants to take their energy management more seriously.
CLG are to be congratulated for having the courage to implement DEC.