Sounds like it they need re planting, you can either replant the whole thing straight from the pot and water well in or you can give them a feed now keep well watered and in the autumn you can divide and make 2 or more new plants.

If you mean Marguerites, they usually do pretty well in pots - are the pots big enough and are you watering regularly, despite the rain? Yellowing sometimes happens when the weather is very cool, these plants are not hardy at all.

Sorry I am confusing with Shasta daisy. I have both so I should have got it right lol.

I'd put them in the ground, as they like the ground quite moist, and probably are drying out too much in the pots. I think plants do better in the ground, as the roots are not restricted. If it's shasta daisies you're talking about, they will definitely need putting in the ground as soon as poss. Annie

You might want to transplant them into bigger pots, and then bury the pots in the ground. They will get many of the benefits of being in the ground, but will suffer less shock when you take them up in the winter to put in the greenhouse.