Tessera Sanitaria (Rome)

Good morning all
This is my first post as I haven't been with you long.
I'm looking for some guidance ref the Tessera Sanitaria, this is directed mostly to those ex-pats in Rome from the UK (Scotland).
How do I get this? Does it coincide with the S1 that I have just applied for?
Any and all information, help would be much appreciated. I haven't arrived in Rome yet, will be living there from December this year, but I would like to get as much organised as possible (have all information to hand) before I move.
Thanks very much