UFO sighting , Shipley, Yorkshire UK

I'm a plane spotter and was curious of a plane flying overhead. As it was I couldn't see it but caught my eye on an object flying to and fro between the clouds. At first I dismissed it as a bird. But it was the speed and the way it was flying that was a concern to me. The white round in appearance object darted backwards and forwards through the clouds. For some time I would lose track of it, but then it would suddenly appear in another place. then back in the clouds and out again. Then in a clear part of the sky it moved at a tremendous speed in a straight line for a while before disappearing in the clouds. I waited and watched for it to reappear which it never did. This sighting went on for about 3 minutes in all.I am absolutely convinced this was an object I could no identify as earthly. I wanted to get my camera but was afraid I might lose so watched as much as I could hoping I might get a clearer view of it.