No Graduation in the UK?

[Brian]

After the age of sixteen (GCSEs or O-levels) many students stay on to 
take A-levels at age 18, in fact by 2015 the minimum school leaving age 
will be raised from 16 to 18.

As for options if you don't do well.
There are further education colleges and adult education colleges which 
aren't usually free, but not expensive.
I passed my O-levels, but left school rather than stay on for A-levels.
Years later, I took some A-level equivalent exams at a local college 
(studying part time) to enable me to take a law degree at university.
So there are always options

Brian