Last year I regularly saw a pair of peregrines over the white cliffs of dover - obviously thought they were bluebirds! However, this year there has been no sign of them - do they migrate and return each year to the same location? If so, I'm afraid they are no more.....

You don't say what time of year you saw them and was it in fact a breeding pair or just two birds seen at the same time?   

They use regular nest sites which have features that suit all their requirements - as many long deserted sites providing these requirements are now again occupied. Often there are a number of alternative nest sites in the same general area which can be seen by the birds from the same look-out points. So not seeing them flying in exactly the same spot, does not automatically mean that they are no more.

The birds both adults, young and wandering strangers do visit these sites and use the look-out points in the winter as part of a larger home range, although most wander off. Hasting to Dover is a bit far for the breeding range of the same pair but could easily be the size of their much larger and over-lapping winter hunting range.