No, BA are specifically not allowing this. Your bags will be offloaded in bulk to a courier and if you go there now, they can't really allow you to search the several miles of warehouse corridors to find your item. Admittedly the airtags may make that a fairly swift process, but it's not going to happen. Very, very occasionally BA will invite you to the baggage area, for example if the item is something couriers won't handle (such as some chemicals).