Make sure you include all of the items you wish to complain about in the initial letter. Keep the content detailed, if you are unsatisfied with the outcome of your complaint, you can go to the next level and that is to contact the Ombudsman. They will only investigate the content of the initial complaint; you are unable to add items later.
This is what should happen during the complaint, quoting from Stafford District General's complaint's procedure:
5.3.4 Ensure witness statements are taken, duty rotas are obtained, medical records are accessed and copied and workplace diagrams drawn if appropriate, with copies attached to the final report. All other documentation must be completed at this time with copies attached where necessary.
Ensure that the investigation process is completed, where possible within 15 working days or receipt.
5.4.5 Take immediate action where failures have been identified to reduce the likelihood that further harm to other patients/carers will occur in the future.
5.5.8 Obtain all correspondence relating to the complaint on completion of the investigation and following approval by the divisional manager. Append all correspondence to the electric file stored within safeguard. Present the report for the Chief Executive Signature and approval.