Bush vetch (Vicia sepium) is a member of the pea family and is a climbing plant using tendrils to cling to its host. It is not bush vetch because it forms a bush but because it is found in bushes where it grows up using the bush for support.
Amongst vetches with the classic pea flower bush vetch is fairly distinctive because the flowers are larger than most and tend to form in clusters a bit like a clover. Each flower starts as dull shade of purple that then turns blue with age and so often a plant will seem to have two different coloured flowers with several shades in between also present. It produces pods after flowering which turn black when ripe.
Flowering as early as April it can go on producing flowers right through until November. It is quite common and can be found in hedgerows and scrubby places where there are bushes to support it. It is popular plant with insects with bees and bumblebees very keen on its nectar and beetles, weevils and other creatures feeding on the leaves and seed pods.