As NHS England suggest
Most NHS care and treatment goes well but sometimes things can go wrong. If you are unhappy with your care or the service you have received, it is important to let us know so we can improve. There are two ways to tell the NHS what you think:

• Give feedback
• Make a complaint
  “How do I feedback or make a complaint about an NHS service?” NHS England website. Retrieved 9th November 2022

Simple feedback is as helpful as making a formal complaint if you want to improve a service. This is quick and easy to do. You can leave direct feedback for many NHS services either using their “friends and family test” or their suggestions form. In the case of GP practices these forms will be available on their practice website.

There is further information on simple feedback with the friends and family test, see under

• Friends And Family Test

As the NHS suggest
“If you’re unhappy with an NHS service, it’s often worthwhile discussing your concerns early on with the provider of the service, as they may be able to sort the issue out quickly. Most problems can be dealt with at this stage, but in some cases you may feel more comfortable speaking to someone not directly involved in your care.”
How to complain to the NHS – NHS

As the NHS suggests
“You can either complain to the NHS service provider directly (such as a GP, dentist surgery or hospital) or to the commissioner of the services, which is the body that pays for the NHS services you use. You cannot apply to both.”

Directly to the organisation (service) you want to make a complaint about

All NHS organisations including GP practices will have a complaint process, details of which you can find on their websites. You can make any formal complaint direct to the organisation (health care provider). This will normally give you the quickest response as it is direct and does not involve going through a third party, such as the local integrated care board (ICB).

Indirectly to the commissioner, who pays for the service you want to make a complaint about

If you do not wish to make a formal complaint to the organisation (health care provider) you can instead contact the commissioner of the service. This is the organisation that pays for the service or care you received. Who the commissioner is (and so who to contact) for various services is explained by the NHS website
How to complain to the NHS – NHS

The Buckinghamshire, Oxfordshire and Berkshire West Integrated Care Board explain in detail who you can complain to for various local health related services if you are not contacting the organisation directly
Make a complaint | BOB ICB

SUPPORT WITH MAKING A FORMAL COMPLAINT

There is significant support to help with making a complaint and this is covered below:

From NHS England
Giving feedback or making a complaint about your health care – easy read NHS England » Giving feedback or making a complaint about your health care – easy read

Further support from NHS England for children and adults who are autistic or have a learning disability, their families and carers
Ask Listen Do – feedback, concerns and complaints NHS England » Ask Listen Do – feedback, concerns and complaints

If after the whole complaints process you remain unhappy with the response from the organisation you have complained about, you can consider taking your complaint further to the ombudsman. This is explained below in more detail with links to the Ombudsman.