Varies from University to University and course to course- some will all be on final year, some will be a 50/50 split of 3rd and 4th, some will be 20/80 and so on. Its not common for anything in first or second year to count towards your degree. At Glasgow, a first is 18/22 or above, with a 2:1 being 15/22 and a 2:2 12/22. If you get less than 9/22 in your final year they are likely to fail you for 4th year, meaning you will be given a general (non-honours) degree. This equates to about 84/70/57% respectively, which is an average across the weighted modules. Strathclyde and Caledonian are a more straightforward 50/60/70%, but I've no idea how Stirling works I'm afraid.