If you are ill while away from home or if you are not registered with a doctor but need to see one you can receive emergency treatment from the local GP practice for 14 days. After 14 days you will need to register as a temporary or permanent patient.
You can be registered as a temporary patient for up to three months. This will allow you to be on the local practice list and still remain a patient of your permanent GP. After three months you will have to re-register as a temporary patient or permanently register with that practice.
To register as a temporary patient simply contact the local practice you wish to use. Practices do not have to accept you as a temporary patient although they do have an obligation to offer emergency treatment. You cannot register as a temporary patient at a practice in the town or area where you are already registered.
More information can be found on the NHS.UK website as well as the GMS3 Temporary services form.