I’m really conscious that fabric first build is essential, as we know already our current new build homes are thermally efficient. With this in mind, I am concerned with over heating. Are there cooling options in conjunction with air source heat & hot water pumps?

Yes – there are heat pumps capable of both heating and cooling. Heat pumps are actually chillers in reverse. You will need to make sure to select a heat pump capable of this in the first place – ask your installer. And you need to make sure your emitters are capable of emitting cool as well as heat. Condensation on pipework can be a problem and normal radiators are not a good type of cooling emitter. Convector radiators are good.