Decided to go to Nissan in the end and get the Nissan green AntiFreeze and I mixed it 50/50.
Complete drain of the yellowish looking murky liquid, a few flushes using the drain plug and air relief valve and fill up again. Noticed a lot of limescale in the radiator header and limescale at the bottom of the water reservoir.
The info from Nissan suggests to fill up until the air is bled out, put the screw in, top up, leave the filler cap up then switch on the engine and rev at 2000 rpm until the lower pipe gets hot.
The lower pipe never got hot, the top pipe was roasting, and the radiator just kept bubbling over. I don't think it was boiling.
Got a bit worried by that.
Anyhow thought stuff it and put the filler cap on and drove about 1 mile and noted that the temperature guage went up at least over half way mark. Bit nervous.
Came back after an hour, the reservoir level went right down and driving for a couple of miles, the temperature stabilised. The lower pipe is also warming up nicely.
I would have suspected the thermostat if it wasn't for the top pipe getting hot. I would have suspected the water pump if it wasn't for heating in the cabin.
I suppose this may have just been an air bubble or something?