Hi Sid the peppers you see in the supermarket are the ones that have passed the 'shape, size' requirement. Your peppers are just fine and are just as usable as any pepper on sale just not as attractive or large. You may even find they taste better!

Mine are still really slow this year, I usually have a really good crop, I changed to a mixed colour variety, not sure if its that or the extremes of temperatures we've been experiencing

I've been growing the long pointy grill peppers in previous years with success, bell peppers are quite big and take a long time to mature, like Mg says the supermarkets only choose the perfect shapes.....homegrown have the taste

Moon - yes, I fully appreciate that, my question is "why".

Pam - I've grown peppers for some years and always seem to have the same problem....

Commercial growers of bell peppers use huge polytunnels to grow the peppers in and, in fact, the majority of peppers in supermarkets are shipped in from Spain and the like. Our summers aren't really hot enough to produce large peppers.