If you have time to spare and plenty of patience then try trawling the DEFRA website www defra.gov.uk - follow links for animal health and welfare then look at the links for stuff like movements and ID.
Rosemary has given you the basics - tagging rules keep changing so best check on DEFRA for the latest advice.
As long as you have a CPH number, keep records of every sheep moved onto / off your holding, keep records of every medicine administered to them, and ensure that each sheep is properly tagged then you won't go far wrong.
How many sheep are you getting BTW? And what breed - I'm just being nosey here