Pretty sure the platter doesn't make them standard rated.
That is specifically one of the indicators of catering supply as defined in VFOOD4140 - Excepted items: Catering: What is catering:-
"Is there an element of service provided to the customer? This could vary from a full waiter / waitress service to simply laying out sandwiches on a platter. The more significant the level of service, the more likely that the supply is that of catering."
Which is why I mentioned it, simply buying a platter of sandwiches from a supermarket does not constitute a catering supply (Safeway Stores [1997] STC 163) but asking your local sandwich shop to provide a buffet or sandwiches on platters for instance does, and is standard rated.