Also known as the European Night Crawler, this is one of perhaps 10 or so species * you may come across in the garden and one of the most common. There does appear to still be some confusion over the Latin name for this species, which changed in recent years from Dendrobaena veneta. We have read now in numerous locations that the correct name is indeed Eisenia hortensis.
This is becoming a popular worm for composting but its likely to be in most gardens regardless. Indeed the individual above was found in the compost bin.
* Chinery, M. (1977) The Natural History of the Garden. Glasgow: William Collins Sons and Co.Ltd.