A few years ago I was stuck in slow moving traffic one morning while travelling out to a school (that was back in the days when I used to go as far over as Rogate). A hawk suddenly stooped onto its prey on the fairly narrow verge right by my car - whoosh. That blew my concentration for another mile or so.
Today I was coming back when I saw a hawk hovering just over the hedge beside the road, a mere ten feet high. Left a bit, right a bit, up a bit, down a bit... I wish I could have stopped to watch....
A bit searching on Google makes me think it was probably a kestrel - although they have brown plumage on their backs, their undersides appear to be mainly grey.
"when hunting, the common kestrel characteristically hovers about 10–20 m (33–66 ft) above the ground, searching for prey, either by flying into the wind or by soaring using ridge lift. Like most birds of prey, common kestrels have keen eyesight enabling them to spot small prey from a distance. Once prey is sighted, the bird makes a short, steep dive toward the target. It can often be found hunting along the sides of roads and motorways."
Although the hovering picture is blurry, it corresponds very well to what I saw as I drove past.