Thanks Franz and Maggi for your comments.
I collected the seed from my own plants of Androsace carnea ssp laggeri which were relatively small plants resembling the plant in Magnar's photo. The original plants are tight cushions with numerous rosettes and did not flower particularly well (no flowers at all this season). The offspring (photo in posting) grew into larger-leaved more vigorous plants and flowered profusely so I suspected hybridisation with Androsace sempervivoides which is the only other species I have. I can only surmise I fed the second generation plants better.
