Can we still use our head office location for back-to-back trades (where we don't store the material)?

No, you cannot use your head office location for back-to-back trades where the material is not stored there.

If you are a seller initiating a back-to-back trade with stock physically located at one of your sites, you must use that specific site, not your head office. On the other hand, if you're a back-to-back trader selling stock that is held at the seller’s site, the material will automatically be linked to that site. You won't need to manually select a location, as the system will automatically associate the transaction with the correct location based on where the stock is stored.