Under the Data Protection Act the name and address of a person making a complaint or any other contact details, will not be disclosed.
If you have been asked to collect evidence to support your complaint, the Council may wish to use this to demonstrate that there has been a breach of planning control. Such evidence carries more weight if presented by the person who collected it and you may be asked if you are prepared to contribute to an appeal, but you are in no way obliged to do so. Most complaints are resolved without the need for formal action, so in most cases giving evidence will not be necessary.
Formal notices that are served on all interested parties in breach of planning regulations are public documents.