Right, bit of an update, jsut been out now its cooled right down and took it for a spin around the local street, it ran absolutely fine, pulled like a steam train!! The heaters were still blowing cold and it did start to get hot a bit quick so i brought it back in. But while its a lot cooler it appeared to have no running issues??!!

I've checked the header tank, its lost no water at all, and the water has no signs of oil in it, nor do i have any white resedue under the oil cap

Its got to be water pump then hasnt it?