You heat up a pot of tea (or would generally just say you are going to put the kettle on), you do not 'hot up the tea'. The usage is specific, which is probabl

You heat up a pot of tea (or would generally just say you are going to put the kettle on), you do not 'hot up the tea'. The usage is specific, which is probably why you did not notice it or pay much attention if you did hear it. OTOH, it is a very common usage when describing weather or competition. It does not take much effort to do a bit of an online search to see that the comment you were replying to was in fact correct that this term is idiomatic British English. This is not anecdote and is easily demonstrated through thousands of examples that are but a short google search away.