There are four self-sown sallow willows in the window box, all of which have been there for several years and are coppiced each winter.
They all differ quite markedly in leaf size and shape.
Top left is, I think, undoubtedly rusty sallow (Salix cinerea ssp. oleifolia), a common and widespread species in Britain, while the large leaf beneath is goat willow (Salix caprea), also common. The two on the right are probably Salix x reichardtii, hybrids between the first two species, also common.
Detailed accounts of all these species are given in BSBI Handbook No 4, Willows and Poplars of Great Britain and Ireland by R. D. Meikle (1984).