When we applied for permission to build our extension, we got an
architect friend to draw up some outline plans which we submitted with
the initial planning application, these contain very little detail but
gave a good indication of what we were planning.
Once approval had been given, we then needed to apply for building
regulations approval and had to have a more detailed set of plans
drawn up which covered all of the details which I expect you think are
missing from your neighbours plans.
Depending on your local building control office, your neighbour may be
able to proceed on a 'Building Notice' rather than a 'Full Plans'
submission, but if this happens, all of the details will be checked
on-site by the building control officer. Regardless of which method
is used, the BCO will want to examine the work at various stages to
ensure compliance with the regulations. Rest assured, the BCO's are
very keen on checking all of the underground work, especially the
drains.
Just be careful that you are not just looking for an excuse to object
rather than having a valid reason for objecting.