My apologies for the U.S. cultural assumption. See http://www.census.gov/prod/2004pubs/p20-550.pdf for what it's like here. I also presumed we're discussing those who finish college, not those who just enter it. What percentage actually finish college in the UK?
The OECD stats look quite interesting. They break things down into Type A[1] and Type B[2] programs. Superficially, Type A are 3+ year courses, Type B are 2+ year courses. Results for the UK and US are here[3][xls]. Executive summary: for the 3-4 year Type A graduates, in the UK, 97% graduate. The OECD average is 67%. This report also has data for the US.
For actual numbers of people in the UK with degrees, there's this page[4] from the National Statistics. For people of Working Age, 18 to 60-ish, in the UK, 16% have degrees, and another 8.5% have "Higher education qualifications". 15% have no qualifications. It would be handy to have data for the 25-35 age range, since not many 18 year olds have degrees.
