Selfheal (Prunella vulgaris) is quite a variable plant, it seems to change with the conditions it is growing in. It can grow in short turf, especially lawns, where it is very small and sprawling which may be a response to cutting or grazing. On bare ground it is a taller, bolder plant although still generally no more than a few inches tall. It is quite common and can be found in many situations although it prefers neutral or acid soils.
The flowers are a purple/blue colour but quickly die off to become brown and they can stay in this state for some time. Withe the flowers being quite small it is not immediately obvious that it is a member of the deadnettle family. Under close inspection it is possible to see the cluster of trumpet=like flowers that are distinctive to deadnettles.
Also known as heal-all it is a traditional remedy for cuts and bruises when mashed and applied as a poultice and it was considered both a cleansing and healing agent. It has a complex chemistry with Wikipedia listing seventeen different ingredients! The plant is also fit for human consumption apparently with the leaves being suitable for use in salads or for drying and making into tea.