Hi Cam,
I believe that for the current year 11 students KS2 fine point score is calculated this way.
Reading+Writing=English and Maths=Maths (English+Maths)/2 = APS for English and Maths
If you click on the top entry in the search result below you will get an excel sheet that does the calculations for you as long as you got the KS2 data.
https://www.google.co.uk/search?q=ks2+2010+marks+fine+levels&sourceid=ie7&rls=com.microsoft:en-GB:IE-Address&ie=&oe=&safe=active&gfe_rd=cr&ei=B70sVcy8DMbH8gf6nYCwDg&gws_rd=ssl
I hope this helps.
Helgi