You asked
Who made the decision to send your post first class rather than second class?
We said
Thank you for your further request for information about our policy regarding the use of 1st and 2nd class postage.
The majority of our post is sent 2nd class, however we do use 1st class stamps to send correspondence of a more urgent nature. Examples of this may include complaints or where there is a need to expedite information within a short time frame, such as some of our surveys which have a limited time frame in which to respond.
More generally, survey operations decisions such as these will be based on empirical evidence involving collaboration between several teams. In this case, decisions about which stamps to use would involve research colleagues (to feed in information about best days for post to arrive), our printing and posting teams (to feed in information from their discussions with Royal Mail or other postal providers) and field management colleagues (to feed in information gathered by interviewers on the doorstep relating to public opinions).
Regarding who made the decision, we would be unable to disclose the information you have requested under Section 40 (2) of the Freedom of Information Act 2000, whereby information is considered exempt if it constitutes personal data.