What kind of tern could this have been? (Sorry, no photo, only a description)

I regularly see terns in the isle of wight, but this one caught my eye, because it looked different and acted differently to the other ones that I see.  It was very slightly smaller than the usual ones I always see, and it was a little bit more white (all over) than usual, and it had an interesting way of fishing for fish - it hovered in mid air, like a kestrel, flapping its wings very quickly as it did this, before "divebombing" for fish.  It was on its own, and made no call.  Sorry I have no photo.