Hello Kate,
If you call the GDC, they will be more than happy to advise and help you.
As far as I'm aware, once you're qualified, nobody can take that away from you. However, if you are qualified and practicing you need to be on the GDC Register.
If you decide to stop nursing for a while, and don't register, then when you do decide to come back to nursing you would need to demonstrate current knowledge with CPD. I think someone in another post has mentioned they would need to to catch up with the full 150 hrs, but double check this with the GDC.
All the best