That much depends on the relationship between the local authorities. On the split wards situation, the returning officer responsible for running the parliamentary election in that area must comment on the review potentially undertaken by the other local authority. It very much depends again on what local practices are. The ideal situation for an administrator would be to have full control of all the areas—the subdivisions, polling stations, districts, staffing and so on —as that makes life easier for administrative arrangements. It is not insurmountable; it is purely about the local practice.
It gets slightly more complicated when we talk about combined polls. If you have a local government election and a parliamentary election taking place side by side, that adds to the degree of complexity. If it is a stand-alone parliamentary election, it is not quite as difficult to administer.