You seem to be worried about the occupancy/ need to reside clause in a future planning application. In other words if you can keep your gfs name off the present house when she applies for planning permission in the future she will be doing so possibly on the basis of a need to build a house/not having one already. IF your gf is contributing to your mortgage, then effectively she will be building up an equity in this first house ( although certainly she should take legal advice on the wisdom of doing this in this manner) so therefore effectively she will have an interest in a house. So it really depends on the type of clause that the local council will insist on. These change from area to area and even from time to time. I have seen normal clauses for eg the planning is granted with a stipulation that the appplicant reside there as their ppr for 7 years. I have seen clauses which state the first occupier must reside there for 7 years- which leaves it open to developers to develop a house and sell on that condition. Nobody can look into the future for you. Clauses may be different in your area now- but could change again in the future, so who knows?