There are a couple of threads here in the BRC A&B section that cover some HACCP-related elements, so it might be worth having a quick look at them. Probably a lot of very specific detail in there that won't be relevant, but might spark some useful ideas. Have a look at this one as a starting point: https://www.ifsqn.co...agents-brokers/
Are you already familiar with HACCP in a more traditional sense?
If so, it's broadly the same as that, or at least as close as BRC gets these days with the ever-growing list of hazard types, but the "process" is your supply chain rather than actual manufacturing, so for example the steps in a simple process flow diagram may be something like:
Your suppliers
Transport
Customs clearance (if importing into the UK)
Transport
Your company, and/or external warehousing
Transport
Your customer.