I am due a counselling session at my docs today and the main thing I want to talk about is my partner. But he states he wants to come with me. Would that be allowed?
Ask him to let you attend the first couple of sessions on your own, and then if both of you wish him to come with you for later appointments tell him you are happy for that to happen.
I actually agree with the AB Ed (is that a bad sign?) go to the first appointment on your own and then decide if you want him to go with you to any further appointments.