As frustrating as it is sometimes to posters on here, you have no control over or rights to the answers you get to your questions. If you are not getting the answers you expect or want then you must want a particular answer, which means you already know the answer.
Your question was, "I wanted to know the best approach of connecting to a Garage CU."
Having weighed up all your plans and responses to questions, I too feel Vortigern's response is the route that best answers your question.
A local electrician may be open to you helping by installing the first fix to their design, which may be a good compromise.