I'm not sure what the UK CAA requirements are but here it's as follows:
Type 2 - demonstrated control through diet, exercise, medication with an Hb1ac of under 7.0. The frequency of the blood tests are at the discretion of the regulator's medical board. If it goes above 7.0 your certificate is suspended until such time as you get things back under control. Not sure how many chances you get if this happens.
Type 1 (insulin dependent) - No medical certificate.
Once you've been diagnosed with Type 1 there's usually no going back as it almost certainly means your body has stopped producing its own insulin.
I've not heard of slow release insulin and I'd say taking insulin is not usual for Type 2. The approved (AME) medication for Type 2 (Metformin) is usually aimed at helping the body to take the glucose out of the blood into where it should be. The risk of taking insulin, and hence why you can't work as an ATCO with Type 1, is that of hypoglycemia.
RD