Me again. I pooped into Halfords on my way home to some coolant in case I ran out again.
Ha ha - best you get some Imodium to control that bowel habit!

On a serious note though - are you purchasing Halfrauds anti freeze?

Are you absolutely certain it complies with the VW G12, G12+, or G12++ standards? If not, then you will have just invalidated your warranty. Mixing any kind of "generic" antifreeze with a G12 coolant with cause it to solidify and block the coolant passages.
I then checked my coolant and found it to again be below the minimum level, however every other time Its warned that its below the limit. Whats this all about? Going to top it up with the new coolant and see how I get on.
I am correct in saying it should not be this low?

Whats the ideal level to top it up to?
Actually, that level doesn't look too bad. Basically, as long as there is some coolant in the expansion bottle, then it isnt a problem. I would suggest leaving it, and try to let it "find its own level". My last S4 would sit at about half an inch below the minimum - whenever I tried to top it up, it would just vent it out the overflow, until it sat ½ inch below the mininmum.
Have you actually noticed any "pink" tel-tale deposits anywhere? Underneath the bottom of that expansion bottle is the integral overflow outlet - fiddle around underneath, and see if you get any crusty pink dried antifreeze residue on your fingers.
And maybe the coolant level sensor needs recalibrating too. When you remove the cap, look inside and you should be able to see two metal "prongs" - which is the coolant level sensor. Are both ends below the surface level of coolant?