If you are doing a theatre EICR then you will receive a test pack from the estates management team. You will have to read all previous reports and all work logs for the last year or so. You will also have to be on the register as an approved electrical contractor for NHS estates.
MEIGaN forms are very different to the EICR forms and will have to be filled in, the operating theatre may very well be IT, and that throws even more paperwork. You will also have to do an induction with the works department, the lockout kit you sign for will have at least three locks, one for you, one for your watcher and the other for the duty estates manager. You will have to sign for your rubber mat and use it at all times when in front of the board.
Earth reference bars will have to be tested individually and readings recorded in the test pack, each supply cable will have to be tested for power quality, conductance, volt drop and all percentages recorded on the forms in the test pack. This is normally done by software, if you do it by calculation you will need a degree in applied mathematics. There is an on line calculator for this available from the NHS but you will probably not have access to their tech papers.
If you install to the HTM,s and MEIGaN then you should have all this information to hand. The EICR codes are the same for any install, its just that you will probably be asked for additional test results that are not covered by BS7671.