Thanks for your responses
Unfortunately this is to go onto a site already in production, all the page types already exist with many nodes utilizing them already, so as David said, I'm not sure that solution would work for us.
Similarly from an on going maintenance perspective, is there no form of import/export feature? Say I had created the fields from a base type, but I then wanted to add a single additional field at a later date? Is there anyway I could add it to the base, and it be distributed across all the types that inherited from it when they were created?
Thanks again for your time,