@Pollylocks it is confusing. I have experienced this too, but while I might be able to get away with it once, I typically don't if I repeat eating the same food again over the next couple of days.
This is informed speculation on my part, but here's two possible explanations for why you were able to eat a serving of bread without the expected glucose spike, previously a problematic food for you.
Now that you've been eating a low carb diet for a while, both your glucose
and insulin levels have come down, which means your insulin resistance has lessened. That's good.
But if you add bread back into your daily diet, likely within a few days, or weeks, or months, your insulin resistance may begin to increase again, followed by increasing blood glucose and insulin levels. Or maybe not. Hard to know. Everyone one has their own "tipping point", the point where their carb intake exceeds their body's ability to manage its blood glucose levels.
Another possibility, and I'm going way out on a limb here, is a question: "Has your gut flora, your microbiome, changed over time because you eliminated bread, and other highly refined carbohydrates, from your diet?" There's some thought that the micro-organisms that make up our gut flora can also improve or worsen our type 2 diabetes. Perhaps, because you've been eating more "whole food" types of carbohydrates, your microbiome is healthier too.
A third possibility, and more likely explanation, is that you walked off the extra carbs during your day in London, before or after you ate the bread. Walking uses up the glucose stored in my muscles, which is then quickly replenished by the glucose circulating in my blood. I put this knowledge into practice when I get a high blood glucose reading.
As you pointed out, we're all so individual. Don't know how having bread again will affect you over time. I'm just thinking out loud.
