One at the top is actually chlorotic, so a significant deficiency is implied. And if you have not been keeping the potting soil regularly fertilized this might be expected. Otherwise it would probably be a virus infestation - something strawberries are prone to. Resulting in rather frequent replacement with "clean" (indexed) stock being recommended.

Agree. Nitrogen deficiency - which is quite common when such small containers are used - as the nutrients wash out of the soil every time you water and have to be replaced on a regular basis. The leaves should be a much darker green to be healthy.

Dave

Added a dusting of blood-meal and watered with a mix of water and comfrey very well mixed in a blender. Comfrey is supposed to be high in nitrogen. Thought that would solve any deficiency in N. Have to admit I've never used any store-bought fertilizers - any recommendations? As you can see they have started to flower so is it too late to fertilize for this season?

Thanks to both the above for your quick responses........it's one of the reasons I enjoy this forum so much.