Your GP can refer you to a specialist, if clinically necessary. If you wish to be referred to a specialist in a particular field you should see the GP to discuss.
If you ask your GP to refer you to a specialist, they will probably suggest that you first try various tests, or treatment options, to see whether your condition improves. Generally, you cannot self-refer to a specialist within the NHS, except when accessing sexual health clinics or accident and emergency (A&E) treatment.
A specialist will only see you with a letter of referral from your GP. The letter will give the specialist essential background information, such as your medical history, and it will also contain details that the specialist needs to pay particular attention to.
For more information, read this leaflet about what happens when you are referred (PDF, 596kb)