Many of the lawful bases for processing depend on the processing being “necessary”. This does not mean that processing always has to be essential. However, it must be a targeted and proportionate way of achieving the purpose. The lawful basis will not apply if you can reasonably achieve the purpose by some other less intrusive means.
It is not enough to argue that processing is necessary because you have chosen to operate your business in a particular way. The question is whether the processing is a necessary for the stated purpose, not whether it is a necessary part of your chosen method of pursuing that purpose.
For GP Practices, it is reasonable to argue that processing is necessary to carry out legal duties of providing patient care.