To find out your NHS number, you can usually just ask your GP, because it will be written on your medical history notes.
If you want a new medical card, including your NHS number, then please follow these guidelines. Visit NHS.uk (NHS) and click on NHS Organisations. Find your local Primary Care Trust (formerly Health Authority). You may need to search by using your postcode. When you contact your Primary Care Trust (PCT), ask to be put through to their Patient & Practitioners Service Agency and say that you would like to know your NHS number, or require a medical card.
Registration staff will take all your relevant details: name, date of birth, address and GP and then issue a medical card, usually within two days. The information you give is confidential. You may be asked to confirm selected personal details in order to verify your identity.