The purpose limitation principle specifies that personal data shall be collected for specific, explicit and
legitimate purposes. 

This means that personal data should only be collected if it relates to the purpose of the processing that we need it for and that we cannot then decide to use this personal data for a further purpose.

We therefore need to be specific in our reasons for collecting the personal data in the first place and if we are collecting for separate purposes, we need to be transparent about this at the outset in order that the data subject is fully informed.