Saw a UFO while flying to Poland

I saw very unusual object while flying to Poland a month or so back. The first was keeping pace with the plane, at a guess around 300ft below the wing. It was there for a good 10 minutes and two other passengers also saw it, before it vanished. We just put it down to being another plane or something. Then 10 minutes later we saw another object in exactly the same place, only much brighter. It was there for only a minute or two, then just vanished like the first. It was definatley no reflection on the glass etc, but we do not know what it was and we did not have anything to film it. Both objects appeared oval in shape, the usual UFO stereo typical shape lol.