Hi, thanks both of you for your suggestions. Nothing unfortunately worked, however I when I was going through some in game settings I noticed an error on my part which I didn't think would be a contributing factor to the flicker but rectified anyway. I realised that when switching out my shader profile for a new one, that at some point when I last played I must have taken them out completely and turned MSAA and Post Processing back on but forgot to turn them off again when adding the shaders back in.
Turning them off and then running around Haven for 30 minutes and so far I haven't seen a single instance of terrain flicker, which considering I couldn't walk more than two steps before without seeing it, is something. Whether that was what was causing it I don't know and i'm fully expecting it to rear it's head again but so far, it seems to be gone.