I noticed the .uk in your name and now I’m wondering if British blackberries have smaller seeds? Some of the blackberries around here (Tennessee/us south in general) have massive, and incredibly hard, seeds. We’re talking 1/4 the size of a pea. But the berries themselves are also huge. Size of my thumb or bigger.

I don’t spit them all out, but there’s usually a few big ones left stuck in my mouth at the end. They’re too tiny to swallow though, so it’s easiest to just spit them out.