Yes there would... people buy cups of tea on their own, or with other products. But something labelled as "Afternoon tea" I would expect to include a cup of tea.

I live in Cornwall. We have the same thing here... normally called a "cream tea". It always includes a cup, or more often a pot, of tea in the cream tea price. There is always cup/pot of tea available separately on the menu for those that want a cuppa but don't want a "cream tea". Same thing. If people started serving up cream teas but without tea to drink it would cause no end of confusion and annoyance I expect. A cream tea ALWAYS includes tea to drink or it isn't a cream tea.