1SL has stated that with pool of just 30,000 sailors he won't have the manpower to manpower for 2 carriers except in an emergency. The idea is to rotate them and that is what will happen.
The interesting question is what will the RAF use to replace the GR4. Given that we have just spent the family silver on Voyager. I suspect it will probably end up being a mixed order over time for B (first) followed by A. We will see.