This tries to give a comparison to GCSE grades although I think it overstates them as GCSE English also requires lots of controlled assesement work on books, poems and plays
http://www.bestpractice.uk.com/skillsforlife/
Entry Level qualifications are below GCSEs, E1 is for speakers of other languages or those with low reading/writing ability, moving up to E3 which is classed as pre-GCSE. Then you move up to Level 1=GCSE grades D-G or equivalent such as Btec introductory diplomas/certificates or NVQ Level 1. Level 2=GCSE Grades A*-C, NVQ 2. Level 3=A Levels or similar. Same for maths. I worked in a school where most students were on Entry Level qualifications.