I can highly recommend getting your own monitor to use at home, as Hurdity suggested. I have WCS, even though my GP is lovely and we just often sit and chat, but when she takes my BP it is always high. Now I just monitor it at home for a week or so before my appointment, jot it down in a little notebook and show it to her, and she's happy. My BP is also naturally on the low side too, just like my father, while my mother always had high BP, so it's something I do need to monitor, especially being on HRT.
White coat syndrome is very common - even with doctors themselves. My GP loves to tell the story about her practice partner. They were just chatting in her office one day and he said he hadn't had his BP taken for a while, so she offered to do it for him. The reading was through the roof. So she tried again with the same result. He tested it himself a bit later and it was fine. I joked to her that the common denominator with his WCS and mine is her!!!!!