Children and adolescents with type 1 diabetes need regular insulin injections or continuous insulin delivery with an insulin pump in order to keep blood sugar levels normal. The investigators know that keeping blood sugars in the normal range can prevent long term diabetes complications involving the eyes, kidneys and heart. However, achieving treatment goals can be very difficult as the tighter the investigators try to control blood glucose levels, the greater the risk for the young person to develop symptoms and signs of low glucose levels (hypoglycaemia). This is a particular problem at night. One solution is to develop a system whereby the amount of insulin injected is very closely matched to the blood sugar levels on a continuous basis. In a closed loop system, for example, a continuous glucose sensor communicates with a computer algorithm which drives an insulin pump. The investigators have been developing such a system in Cambridge over the last year with funding from the Juvenile Diabetes Research Foundation. The investigators have found that this system is very effective at preventing hypoglycaemia in young people with diabetes.