Perhaps something like: 'I'd really appreciate it if you could try to be on time for appointments'

My dear colleague; continual lack of punctuality could be the cause of termination of your employment with this firm.

Simple and to the point is; 'Our next appointment starts at 13:00.' But an appointment is different than a meeting. If the colleague is always late for meetings you can be much more direct. Dan Smith has the correct solution (shut the door).

Hi Iris, OK, for one on one situations as such as this, once you have finished discussing what you met for and it comes to arranging the next appointment, simply say we shall meet again at "11am sharp". Emphasis on the "sharp" and the latecomer who will know he/she is a latecomer should take the hint. This is probably the most informal way of dealing with this kind of person. If the situation persists what you need to say is that you have further appointments after your next appointment with the latecomer and simply ask them to be on time please, so long as you use the word please it will be taken as a polite request. You could also say "would you mind being on time for our next meeting please" as I have a busy schedule. It depends on the situation but there are many ways of dealing with latecomers in a polite way. Hope that helps :)

For a meeting of several people, simply close the door at the appointed time. (Don't lock it). Nothing needs to be said but the latecomer needs to open the door and will understand that they are late and that the meeting was started without them. One on one is difficult. I don't know a good way. When the actual message is unpleasant, it doesn't help much to say it nicely--it may even make it worse.