Hmmm .... I believe you can operate a business from home, claim an appropriate percentage of light and heat etc and still avail of full PPR entitlement upon selling your PPR.
The key thing here is that the space used for th work should be fully capable of being used as a resiudence also i.e. I have always advised clients to store their golf clubs under their desk, encourage the kids to play in the room ar various stages throughout the day, definitely in the evenings and weekends.
The difficulty is where there is exclusive business in a room in the house.