Hi Harold, and welcome,
I hate to break it to you, but everything you ate yesterday was carb-heavy. (Cornflakes, honey, rice cakes, bread, crisps, rice and BBQ sauce and the sugar in your coffee). Almost all carbs turn to glucose once ingested. So when you say you aren't a "typical person who brought this on with poor diet"... Nah, I'm just messing with you. Well, up to a point, anyway. The thing is, the foods you mention are perfectly fine for a lot of people. And then there's the lucky few, like you, like me, like your family members, who are genetically predisposed to develop T2 diabetes on a high-carb diet. Our bodies just can't process it, and after a while it just can't keep up anymore. It's a kick in the head, eh... All these decades we've been told the carby stuff's good for us, it's on the EatWell Plate and everything... They told me to cut out fats and triple my carb intake at the hospital; it left me morbidly obese and a raging diabetic, just about on death's door. So while people tend to get the wool pulled over their eyes about a one-size-fits-all diet, there's a diabetes pandemic going on. Lovely, eh?
That does mean that there's a massive amount you can do yourself to get your blood sugars back down. Just cut the carbs, up the protein and fats. I know, I thought that advice was insane too, but it made my blood glucose drop like a stone! That last bit is important, though: if you do start cutting carbs, well, you're on gliclazide... And a low carb diet with gliclazide can result in hypo's. So you'd have to change things very carefully and keep in touch with your doc about the dosages you're on. I was on metformin first, then switched to gliclazide, faceplanted with hypo's a few times as noone told me low carbing'd have to be done with care if medicated, and then my GP stepped in and took me off of everything. I've been without diabetes medication since, and in the normal range until recently, when my HbA1c went up a little due to another medical issue, but is dropping again to non-diabetic levels, as things are getting sorted. All this to say I've been on the same meds as you, and managed to get rid of them in three months, by changing the way I ate. So should you be interested, you might want to read a little here on the forum (success stories'd be a good place to start), maybe dietdoctor.com as well. Just be really, really careful and test a lot.
I have to be honest though... If you're seeing 14's on a high carb diet with medication, I think you'll likely not need it for much longer should you go low carb. Can't promise anything of course. Just can't stress enough to be careful if you do change things around. Hypo's are NOT fun. As for when the meds work: Metformin takes a while to get doing, so give it a little while, but it doesn't do much of anything about what you ingest. It makes your liver dump a little less glucose (which it does when you wake, or when you're stressed or ill), and makes you a smidge more sensitive to your own insulin. Gliclazide on the other hand, forces your pancreas to excrete more insulin. As T2 diabetes isn't a matter of too little insulin, but there being so much of it you've become insensitive to it, it is kind of putting out fire with gasoline. It works, but it doesn't solve your insulin insensitivity. So there's a couple of options: You medicate and leave it at that, you change your diet, or you do a bit of both. Try to find what fits you, your body and your life/-style, as there's no cookie cutter type of answer. We're all different, and what one needs could be entirely different from what works for another.
Good luck!
Jo