From Wikipedia: Tradescantia fluminensis is a species of spiderwort native to South America. It is one of several plants known by the common name Wandering Jew. It is also known as River Spiderwort, Small-Leaf Spiderwort, Inch Plant, Wandering Trad, Wandering Willie and Wandering Gypsy. Forming a dense mat underneath forest tree cover, it smothers ground-level plants and prevents the natural regeneration of taller species and if left unchecked, it can lead to the destruction of native forests.
Found escaping from a neighbour's garden.