Resolution Issues - Using LG 40UF770V TV as monitor for rMBP 15" mid-2014

Resolution Issues - Using LG 40UF770V TV as monitor for rMBP 15" mid-2014.

I recently purchased this 4k TV for use as a monitor. As I understand it, it should support 3880x2160 @30Hz via HDMI and @60Hz via Mini DisplayPort, as per this article: Using 4K displays and Ultra HD TVs with your Mac - Apple Support

The very first time I connected the TV via HDMI the resolution showed, and ran at 30Hz as expected, but since then the maximum resolution offered to me is 1080p. It appears that the system has convinced itself the TV is only a 1080p screen(see screenshot).

I have tried a number of solutions but to no success.

So far I have tried.

1 Resetting PRAM and SMC

2 Deleting display settings and preferences

3 Using custom resolution apps like SwitchRes and Display Menu

4 Using 'option' to show additional resolutions in display preferences

5 Resetting TV to factory settings

6 Using windows via Bootcamp to set resolution

The TV is this http://www.lg.com/uk/tvs/lg-40UF770V

If anyone has any ideas how to solve this I would be very grateful, thanks.