Wow Stu, quick reply.
What you've built is basically what I'm after, but from what I've read the Cube can be temperamental.
I do have RPi somewhere, so to have a play I may get a CC1101,
MAX! Wireless wall mount thermostat - BC-TC-C-WM-4 / 131651
MAX! TRV - BC-RT-TRX-CyN / 142016A0A
I would like to control the system from my mobile so if I'm out late there's no point in the heating being on. There are some HomeMatic apps out there which work with openhab etc, but maybe using your web interface would be easier.