For heaven`s sake don`t start digging them up just because they`re in flower, because the fact that they are flowering means absolutely nothing at all with regard to potato production.
With regard to the Arran Pilot, there are many first early varieties which don`t flower at all (I can`t remember whether Arran Pilot is one of them), but all you need to do is remove some of the earthed up soil from around them with your fingers and probe among the roots to feel for spuds.
As to the 2nd early and maincrop, they will all flower, but the flower production has no connection whatever with potato production. The plants will let you know when they have made all the tubers they are going to by the tops simply dying back, and they will not be fully mature until this happens.
Furthermore, they probably aren`t going to be ready until after you`ve finished the Arran Pilot anyway.
When you`ve dug all the Arran Pilot, then you can think about the Kestrel, but if you want to keep them then you must leave them in the groiund for a full 2 weeks after the foliage has died down or been cut back, or the skins won`t set, and they won`t keep.
Leave the Desiree and Majestic until they die down on their own, or until you have to cut the foliage back for blight
