Hi Starain,
Because of Britain's mild winters, most of our raptors are resident as they don't need to migrate. The only migratory species are fairly scarce: Osprey, Honey-buzzard, Montagu's Harrier and Hobby (summer visitors) and Rough-legged Buzzard (winter). These five also happen to be species which tend to migrate on a broad front, not concentrating at particular points. The final problem is that large raptors don't like to cross water: the North Sea is too wide for raptors to cross comfortably, so by and large, they don't.
There are some far better raptor migration points further east in Europe, where the continental climate means winters are much colder, forcing birds to migrate more. The famous ones are:
Falsterbo, at the southwest tip of Sweden
The Bosporus at Istanbul, on the crossing from Europe to Asia between the Black Sea and the Mediterranean
Southern Israel, the crossing from SW Asia to Africa
Michael