Contributor or respondent
For ONS surveys, use “respondent”.
Enquiry or inquiry
An enquiry is a question. An inquiry is an investigation.
Annual Business Inquiry
For surveys, use “survey”, even when referring to, for example, the Annual Business Inquiry.
This term has a specific meaning in statistics. Do not use it in a statistical context unless you have a particular point to make about the statistical significance of an estimate. If you do have a point to be made, always write as “statistically significant”.