Staither, as you have a friend here in the UK you could ask them to speak to their clinic or doctor to see if they can give any information about insulin provision.
There must be some provision within the EU for health care for workers who need insulin, so perhaps they can find out on your behalf before you leave.
Usually you need to go and register at the clinic or doctor's surgery, with your card and also some proof of your address in the UK - though I think there is some allowance made for recent arrivals who might be staying with a friend. You fill in a form and are put on the register.