Given the writer lives in Britain she would do well to forget about farmed berries and forage for wild blackberries instead. Urban, suburban, rural, they're everywhere. They're bang in season at the moment and my wife and I are getting half a kilo (a pound) in about 40 mins of lazy picking in the mornings before work. They are absolutely delicious and freeze well for cakes, crumbles and such in the winter.
Anyway, they are delicious, but we've had ridiculous amounts of rain this summer. All the rain seems to have made them flower and grow earlier than usual and die off much faster. Normally there's fruit for about a solid month. I think we barely got a week this hear :-(
Come to think of it, the wild plums are usually ripe at the end of August. I should go check that they aren't also ripening early, because they don't last long.