You have 3 years from when you complete the 14 exams.
From the CAA's website,
LASORS Section J
A pass in the ATPL theory examinations will be
accepted for the issue of a CPL or IR during the 36
months from the end of the month of the date of
the
final pass in the examinations. Provided that an
IR is obtained during this period, a pass in the ATPL
theoretical knowledge examinations will remain
valid (for the purpose of ATPL issue) for a period of
7 years from the validity date of the most recent
renewal IR entered in the CPL. However, if a
professional licence with IR is
not gained during the
36 month period, the
ATPL theory credit will lapse.
Candidates would have to re-pass the ATPL or IR
theoretical knowledge examinations before an IR
could be granted.
Be familiar with the LASORS, in particular Section G and J.
You can find them
here.