Given that nursery is at most 2 years and is often at a location other than the primary school, I would have thought that the least disruptive thing - looking at the whole school population, would be to move the the nursery.
Ds went to a primary school which had no on-site nursery. Even if there is an on-site nursery - does every P1 go to that nursery. The fact that that isn't the case, demonstrates that an on-site nursery is not a necessity. Sufficient nursery places within the catchment, yes, but on-site No.
I agree with TheBogQueen that it is a far greater disruption to make P7s effectively itinerant - and extremely unfair on them.
Re the GP rooms - that unfortunately is the nature of our schooling system. Unless and until gp rooms become mandated, they will always be commandeered to become classrooms. The only way around it in new builds would be to deliberately design gp rooms that were unsuitable as classrooms (too long/strange shape/too narrow) 
In ds' primary school, the enrolment nearly doubled during his time there (no school closures in the vicinity, just a combination of birthrate and placing requests), so it progressively lost its noisy/quiet room, its computer room and finally its library
- and also had to have staggered lunch and play times. Every single square inch of that school was used - sometimes many times over. Not everything could be stored inside so there was a container for books etc outside.
Visitors waiting to see the head teacher (or any other teacher) had a small bench outside the small office in an area which also doubled for structured play.
The space was so tight that if parents wanted to withdraw their kids from SHRE classes (which, as a school with a high Muslim population - some of whom were quite fundamentalist, was a likelihood) the head had to say that while it was within their rights to withdraw them from the class, the children would have to be picked up for the hour and returned afterwards, as there was literally nowhere in the school to put them while the SHRE class was going on.