I'd say the ones you've mentioned would be better in their own pots, specially the rosemary and parsley. Lemon thyme often doesn't make it through the winter at all, and certainly not very well, but can be mixed in a pot with other small herbs that don't get too invasive or large, like maybe other thymes or marjoram.

Thanks for the tips Bamboo, I think I'll give my Lemon Thyme another go in its own pot and see how it does through the summer. Sarah