Lots, if you are packing yourself, then EH will need to approve your premises.
On labelling, you'll come under the Food Labelling Regulations 1996 (FLR) which say you must describe the product correctly eg “leg of pork” is leg meat from a pig, it must have a weight that is correct (both not over or under – EH usually approve your scales), have a use by date that has a logic behind it, and any storage instructions relevant to that (eg keep refrigerated if your use by date assumes that it is kept in a fridge). Where there are additional ingredients, these must be listed (but some are allowed to be excluded) in QUID order.
You’ll also come under the Meat Products Regulations 2003 for your sausages, with a sausage needing to contain at least 32% pig meat, and if you are going to call it a “pork sausage” then at least 42% pork meat. Having said that “meat” is defined by EC directive 2000/13 as amended by directive 2001/101 as “Skeletal muscles of mammalian and bird species recognised as fit for human consumption with naturally included or adherent tissue where total fat and connective tissue do not exceed”...fat 30% connective tissue 25%.
So a pork sausage can consist of 42% meat, which in turn may only have 45% real meat, in other words a “pork sausage” may actually only have 19% meat, with the rest being fat, connective tissue, rusk or other fillers.