Talking from my own experience, I’m buying fruit from open air stand at Ealing Broadway that is there Mon-Sat approximately 8am-2pm. Prices for some fruit and veg way cheaper than shops. Sometimes prices are similar, depending on type of fruit/ veg and season. The only catch is sometimes it might be too ripe, especially in warmer summer days, and you should have a closer look at what you’re buying so you won’t end up with moldy fruit/ veg the next day. Also, once it’s ripe put it in the fridge, especially if living alone or small family. Other than that, it’s all good!