Usually on diagnosis they take an Hba1c every 3 months until things settle down, once your under control it's done annually. The hospital clinics sometimes take the blood themselves or they may request that you go to your gp surgery and they take your blood a week before your clinic appointment.
Just one word of advice, if they try and move you over to the care of your gp surgery try your best to stick with the hospital diabetes clinic, they are more specialised in dealing with problems surrounding type 1 diabetes.