Thats correct....
Heres what Lasors (download it from the CAAs website, great piece of information) says about it:
A candidate must complete all required written
examination papers within 18 months of their first
sitting, using a maximum of 6 sittings and no more than
4 attempts at an individual paper within the 6 sittings.
The papers can be attempted in any order. A Pass in
an examination paper will be awarded to a candidate
achieving at least 75% of the marks allocated to that
paper. An applicant failing to pass all of the relevant
examinations within the time limits (imposed by
JAR-FCL 1.490/2.490) will be required to re-enter the
examinations as though for an initial attempt.