triciamonty,
If you get permission for a house it won't be "just a field for grazing" it'll be a site with traffic turning movements several times during the 24-hour day.
Back roads have a habit of becoming busier and busier, with poor surface, camber and unprotected ditches.
The comments I made above relate solely to typical [not exhaustive] problems with entrance geometry and turning movements, sightlines and removal of hedges.
There could be any number of reasons the Council might refuse the permission, never mind the entrance.
You would be well-advised to either have the relevant discussions with the Council before you purchase the site yourselves or appoint a competent architect to develop the design and have the relevant discussions with the Council on your behalf.
Remember, the Council in general have no obligation to grant permission for one-off houses not on zoned land.
Even if one of you is the offspring of the landowner, lives in the locality and contributes to the local economy it is not always clear cut.
PPPPP.
ONQ.
[broken link removed]
All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.