You can order as much or as little as you want. For instance, last time I went we (party of 3 ladies) ordered:
Buckingham Palace - Our traditional tea sandwiches, scones and jam tarts complemented by fresh strawberries and cream, or a selection of freshly baked pastries, along with your choice of tea. $19.50 (we ordered just 1 of these, and it gave 1 person their tea - we shared the foods)
English Blue Stilton Cheese - served with walnuts and marinated berries $6.95 (just one order, we shared)
2 more teas ala carte
Pastries $2.75 each - we ordered 3, one for each of us. They bring a tray of them so you can drool over them and decide. We couldn't pass them up!
You can order just one of the big "combo" things if you want to share, and then buy ala carte items, or just tea and some pastries. Completely up to you.