Hi Fluffywoo. Welcome to the forum. I hope I have some good news for you.
Diabetes is defined as a disability under the terms of the Equality Act 2010. This act allows for organisations such as youth clubs to apply something called ‘reasonable adjustments’ in order to avoid what it calls ‘substantial disadvantage’. In the case of the act, this is defined as “something more than minor or trivial.” This can often be open to interpretation, but I think you could successfully argue that to maintain your son’s health, you need to be there with him as the consequences of a hypo, for example, may not be minor or trivial. The disadvantage arises from your son not being able to access the same service as the other children at the club due to his condition unless you are there with him. One of the criteria for assessing what is reasonable is “The extent to which it is practicable for an organisation to take the steps” To allow you to be nearby wouldn’t be a difficult practical step to take. Am I right in thinking that you are no longer allowed to wait in the reception area? If so, where do you wait now?
As others have suggested, speak to your DSN as she may be able to arrange for the club’s staff to have training. Have you told the staff why you need to be there and what your son’s needs are? Often, people with no experience of type 1 have no idea of its complexity and become more flexible when they are told of the reality. If this doesn’t work, give them a friendly explanation of their duty under the act as explained above. This often scares them into compliance without the need to take it further. If you would like me to send you the official document, please let me know. I've written this on the assumption that the youth club isn't attached to your child's school, so please correct me if I'm wrong.