If you are a student member and currently not doing any job, then you can defer your PPD requirements.
Just mail - Quality@actuaries.org.uk
A sample mail :-
Subject - Deferring PPD requirements
I am ______, ARN - ________. I am a student member of IFOA and studying full time under the reduced rate system. I am currently not working so won't be able to submit my PPD this diet.
Kindly update my PPD as soon as possible
Thanks & Regards
Note - They might ask for any proof that whether you are a student or not, in that case just revert them a mail asking exactly what document is required and stating them that you are willing to provide whatever is required.
Since in the mail you have clearly mentioned that you are a student, so most probably it won't be required. If they ask you just arrange the whatever document is required