It is a Silver Saxifrage. The silver comes from the lime encrustations on the leaves of many of the forms. It needs well draining compost with a little lime added. They like a good dose of sun do the silvers, but do not let the pot itself get so hot that it fries the roots. To be honest, Nicholas will eventually get quite big. Mine must be a clump of over 18 inches across, so it is probably better planted in the ground, unless you can give it a bigger and bigger pot. By the way if it does flower (18 inch tall sprays of white flowers about now) the flowering rosette will die. You need to then very carefully take it away without removing the new side rosettes. There are dozens of Silver Saxifrages. I have over 30 different ones and there are a lot more in the National collection.
