Hi Cockneyred, welcome to the forum. The most logical explanation I would give is that as your pre-bedtime bs reading is 4.5mmol/lt, sometime during the night you are going hypo, and your liver is over compensating for this by dumping large amounts of glucose into your system. But as you have been a diabetic for nearly 50 years, I would have thought you would know all the ins and outs of living with diabetes, and this seams to me to be too obvious and answer to your problem.
Is this a recent problem, have you changed something in your daily regimen?