A long bright ball of light shimmering brighter then lower constantly

it seemed to move at a steady pace from over the sea direction with the ball of light shining bright then dim, no noise, did seem to stay in position forabout 30 secs stationary, too high up to be a plane and no red flashing lights to indicate. the craft got extremely bright with colour with an almost purple/ light blue colour hint and then shot off into distace at some speed then disappeared! it was a very clear night and we couldnt see the craft from then.

i tuned into the local london air traffic control towers on a scanner and didnt hear any activity or any air- tower communications to indicate a plane.