This came from our own Smitty McG at another forum. I found it very interesting and wanted to share with the rest of you sausage heads.
I found it on page two of this article;
http://www.hlf-law.co.uk/flashsite/Departments/Regulatory/Food/No in Meat Guidance.pdf
General structure of the legislation
Other than certain traditional products, the legislation limits the use of potassium and
sodium nitrite in meat products to a maximum amount added of 150 mg/kg, and in
sterilised meat products (Fo > 3), to 100 mg/kg. The use of potassium and sodium
nitrate is permitted only in non-heat-treated meat products, to a maximum amount
added of 150 mg/kg, although nitrates may be present in some heat treated meat
products resulting from natural conversion of nitrites to nitrates in a low-acid
environment. The limits for both nitrites and nitrates relate to the maximum amount
that may be added during the manufacture of the product i.e. ingoing limits.