Peregrines are widespread in the UK through the western part of England, and in Wales, Scotland and Ireland. In southeast and east England they are found on a small number of isolated sites, though their range is slowly spreading.
They reach their highest densities in upland areas of Wales, southern Scotland and northwest England. The UK population was estimated at 1,400 pairs in 2002.
In the British Isles peregrines do not migrate, and the majority stay within 100 km of their birthplace, although some upland birds move to lower ground or the coast in winter. While the British and Irish populations mix, there is practically no exchange with continental birds. Some of the migratory Scandinavian birds winter in Britain.
Peregrine numbers declined during the 19th and 20th centuries because of illegal killing by humans, which at times was relentless. Widespread contamination by persistent toxic agricultural chemicals such as DDT caused the collapse of the peregrine population in the UK in the late 1950s.
These pesticides built up in the food chain and concentrated in peregrines and other birds of prey, causing increased adult mortality, eggshell thinning and reduced breeding performance. By 1963-64 80% of the UK peregrine population had been lost. Only birds in the remoter parts of Scottish Highlands were unaffected.
After the banning of these pesticides peregrine numbers slowly recovered, and by the late 1990s reached pre-decline levels over much of their former range. However, in southeast and east of England the bird has been slow to recover, and the range is now contracting again in northern Scotland.