AnneK,
I think you need to talk to your son's doctor/care team as soon as possible. As a type 1 myself, I am not aware of anybody not using basal insulin as a long acting insulin. This is a background insulin usually given once a day (sometimes twice) to cover a 24hr period. I would think that your son's short acting insulin has started to fade by 10pm, and with no basal insulin in the body to cover between injections, blood glucose begins to climb. 16.6 mmol is not good long term, and as he has been diabetic since April, it is time to speak to someone. Best wishes!
Nigel