Gypsy-Moth Caterpillar (Lymantria dispar dispar)

Amazing looking caterpillars. 

Gypsy moth is a moth which has caterpillars that can defoliate trees and shrubs, the European strain of this moth has become established in London and surrounds. The adults are sexually dimorphic (the sexes have different appearances); males have a wingspan of 3.5-4cm and are greyish brown, females have a wingspan of 4.5-6cm and are white with a few darker markings.
It is the caterpillars that are often noticed in gardens as they are up to 7cm long and have yellowish heads with hairy brownish yellow and black bodies. There are also a series of 5 pairs of blue spots and 6 pairs of red spots along the body. Numbers of caterpillars can reach high densities and trees and shrubs can be stripped of foliage.