Dark orb like object occasionally reflecting in the sun hovering in and around a single cloud below departing flight path from lhr and lgw. object caught my eye whilst eating brunch in my dining room with my 2 sons. the weather was partly cloudy with blue sky and a light breeze. the object hovered below a single cloud for 1-2 minutes whilst airliners flew over the top of it. it increased altitude to above the cloud and hovered again. it then descending into the cloud and moved left and right appearing from both sides of the cloud. it was reflecting in the sun periodically as it slowly moved and hovered. it appeared much smaller than aircraft flying above. observed the object for around 5 minutes until lost sight of it. i tried to capture on phone video but object too far for the phone's camera to pick up. at first i thought it was a balloon but it changed height and direction and hovered, it was definitely under power and was not a helicopter.