Just an update, we are settled in now.
The ground source heat pump has been commissioned and is working perfectly, water goes out at 1deg returns at about 5deg, the heat difference is used to heat gas which is then pumped through a compressor which creates the heat. Very clever.
The 2 tanks were filled with cold water about 750 litres, it took 4-5 hrs to heat them up to 50deg. Brilliant. House sits at about 23deg quite comfortably could probably get it up to high 20's no problem.
All feels like free heat, it's actually a 1 to 4 system which means for every 1kw of electric I use on pumps I get 4kw back, constantly because of the stability of ground temp.
I kicked my builder into touch and have arranged for other contractors to come in next week and demolish old house. I'll put up pics.