Hi there. Firstly, do your Employers have you recorded as having a 'disability' under the Act?, I know type 1s come under it automatically but you too are an insulin user (albeit Lantus only but this still could cause you to go low during the day of course). If you do come under the Act then you are right, they do need to make 'reasonable adjustments' but the question of what is reasonable is subjective to a large extent. You are asking for a longer time to eat your food because of your digestive problems, is this ANYTHING to do with your diabetes? If it is, and if your GP can provide the information to support this, then it is possible that your Employers would at least have to discuss the matter with you. This may consist of adjusting your 9.30 break to a 30 minute one and your lunchbreak to a 15minute one for example. IF you require extra time directly relating to your diabetes, for example you feel like you are going low outside of those breaks and need to do a finger prick test, then yes, they would most likely have to allow you to randomly check during those times.
The problem is that ALL of us would be deemed as taking the you know what if we sat there slowly eating 3 bananas and 2 yogurts whilst our colleagues were getting back to work, any extra time we take usually means less time or extra work for others. Please don't get me wrong, of course we may need extra time to take our insulin before our food (although you don't take bolus) and subsequently extra time to check our glucose levels after but to be honest, this for me means a few extra minutes.
Either way, maybe you could arrange a proper meeting with HR and get it all written down, that way it doesn't become a battle every time you have your break. I think most of us have found that there really is a balance between what we may feel we are entitled to and the reality of what we're likely to get. I would say it really is give & take at work and you wanting to 'take your time' to eat would really annoy me as a Manager too, UNLESS there is a medical reason associated with your diabetes in which case get it all recorded.