The Sky HD box just starts showing a blue screen today, after googling I try a forced update;

1. Switch off the sky power
2. Hold the back up button on top of the box and power on.
3. Wait until 4 LED’s light up (this can take up to 30 seconds), the screen should say updating don’t switch off
4. Wait for up to 10mins
5. Box will go into standby give it couple of minutes and see if it comes out of standby

This didn’t work but amazingly this seemingly nonsense set of instructions does;

1. Unplug power lead from Sky
2. Disconnect/connect HDMI from Sky
3. Disconnect/connect HDMI from TV
4. Reconnect Sky power
5. Wait a minute or two
6. Press ‘Sky’ button on remote

Thanks to this post for the tips.