Kevin and I found this little diathus growing in the back lane, obviously very hardy. Z4
Although it fits the description of D. subacaulis best in ‘A-Z’, Googling pictures seem to indicate that is probably closest to D.myrtinervius aka Albanian Pink. Pictures of both give such a range of colour and shape, and written descriptions of colours and identifying features are similarly so varied that it is have to believe only one plant is being described. However I did find a picture which looks exactly like mine, the close-up is of a battered October flower missing a petal or two, but is true to actual colour.
It forms a larger mat than described and has masses of flowers in early summer, with a few in late summer.