Not sure why you want to do an engineering degree if you want to be an RAF ATCO as it would have no benefit, other than the fact that you had achieved a degree.
You say that your main aim is to achieve selection through NATS, yet you then say you really want to get into the RAF. Perhaps time to make up your mind? Neither job would be boring in any way, shape or form.
RAF and Civil ATC are quite different. In the RAF you are an officer first and would have to undertake various other duties, perhaps not connected with ATC. For anyone truly wanting to enter the ATC profession in the UK, NATS is the recommended route.