GCHQ intervenes to secure smart meters against hackers
ft.com
ft.com
Basically it says that all smart meters that were to be introduced in the UK would have shared the same encryption key, which if compromised would have allowed an attack on the grid system. 2 millions installed out of 53 millions planned.
This one seems to have the relevant text though, without going to the paywall:
https://tallbloke.wordpress.com/2016/03/18/gchq-saves-uk-sma...