After running up to temperate to carry a leak test a fair chunk of day was spent trying to find a cooling system fault that would cause high temperature rise!
Finally I found the fault lay in the temperature sensor. The discovery uses a different colour coded sensor than that of the defender, green opposed to black. With it swapped over to the black defender sensor the indicated temperature was back to normal, crisis over.
Slight leak on the inlet side, gasket need replacing. Also need to re-remove intercooler to flush out the excess oil that seems to have built up in there.

Other than that the engine runs and performs sweetly.