You need to get a blood glucose monitor and test before and two hours after foods. Best to avoid high carb food like breakfast cereals, bread, potatoes, rice and pasta. Also avoid fruit juice and fruit like bananas and grapes. You should find your blood glucose reading dropping. Ideally you want 4-7 before and no more than 8.5 two hours after meals.
You need to be careful with gliclazide that your blood sugars go too low and you get hypos once you eat low carb. If so, reduce the Gliclazide. Unfortunately GPs just prescribe pills and allow people to have years of high blood sugars which can lead to retinopathy, neuropathy and various other complications. The experience of people on these forums is that diet is the most important thing to treat type 2 diabetes.