If you've lost your reference number related to a building regulation application, you'll need to have either the reference number or the property details to track your application. Unfortunately, the documents do not provide specific steps for retrieving a lost reference number for building regulations.
However, if your query is about a council housing bidding number, you can retrieve it by completing a form available through the Choices Homes site. Here’s the link to help you out: Forgotten Bidding Numbers.
For specific building regulation issues, it might be a good idea to contact the Havering Council directly for assistance.