Hi Liam,
Assuming it is the PPL(A) you are applying for, the skills test is valid for 12 months as described in LASORS C1.4:
The Skill Test shall be taken within 6 months of completing the flight instruction. All sections of the Skill Test must be completed within 6 months. The Skill Test has a validity of 12 months for the purpose of licence issue.
On the exam side of things you've got 24 months from the date you finished them all (LASORS C1.3):
These examinations contain multiple-choice questions for the most part and are normally conducted under the auspices of a FTO or a Registered Facility. An applicant shall be deemed to have successfully completed the theoretical examinations for the JAR-FCL PPL(A) when awarded a pass in all of the above examinations within a period of 18 months counted from the end of the calendar month when the applicant first attempted the examination. A pass will be accepted for the grant of a JAR-FCL PPL(A) during the 24 months from the date of successfully completing all of the theoretical knowledge examinations.
Hope that helps and you manage to get the RT sorted in time!