I'm posting this in foreign finds as I'm pretty sure it is not a British native.
I spotted this Clubmoss in a florists 'sick bay' - dried and burnt. After a bit of care it seems to have recovered and is flourishing in a terrarium.
I'm assuming it is a member of the Selaginellaceae by the arrangement of the leaves, and my initial thought was Kraus's Clubmoss, Selaginella kraussiana, however it seems both more robust, has fractionally larger leaves which are not minutely toothed. The lateral leaves are approx 2mm long, the alternate leaves on the upper surface of the stem are approximately 1.5mm long with an almost excurrent distinctly upturned nerve extending from the tip.
Any help with ID, suggestions for suitable references or pointers in the right direction would be greatly appreciated.