I have a few Oxlips (Primula elatior) in the garden and will add more. They are woodland plants and seem to grow well on London clay although their native habitat is the boulder clays of Eastern England. When I started planting wild species I had hoped to establish Cowslips (Primula veris) but the clay and partial shade does not suit them. I should have taken note of where Cowslips thrive: open sunny sites on chalk.

 Case in point I saw thousands of Cowslips waving in the breeze on a spring walk last year on the hills overlooking the Vale of Pewsey [See entry dated 29th. April 2019]. The Oxlip is a close relative and every bit as lovely so an agreeable alternative to my original intention.
 Both are related to the Common Primrose (Primula vulgaris). Happily it is indeed common and grows freely all over the place be it country lanes or urban gardens.