Thanks to @i_konst For spotting this new page on the UK SmartThings website which announces that the ADT/smartthings model line should be coming to the UK next month.
This is been available in the US for about a year, and is the only smart things model I personally would consider as a security system, as it is the only one that has cellular communication to the monitoring center. All other SmartThings model lines rely on the Internet and the smartthings cloud for all notifications, including the ones to your own phone. It also has its own set of dual logo security sensors which use a proprietary protocol and should be more reliable than the home automation ones.
I don’t know if it’s going to have exactly the same features as the one in the US, but here’s the discussion thread and a couple of other links for that one.
And one community member has created a popular custom smartapp which has a lot of additional functionality For integrating the home automation and home security sides of this model. I would think it would work the same with UK version, but of course we will have to wait and see to be sure.