When someone has finished 14 days isolation, do they need to see their gp?

No: Only if symptoms appear, but if not maybe just to notify the GP that everything is Allright.

No: If you finished 14 days of isolation and have never had symptoms you shouldn't need to see your MD. If you had been ill, wait the 14 days and an additional 7 days without any symptoms at all before returning to work,etc. Some places may require an ok from their medical department or from your MD, however.